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Message-ID: <516C3264.3050409@citrix.com>
Date: Mon, 15 Apr 2013 19:01:24 +0200
From: Roger Pau Monné <roger.pau@...rix.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>
Subject: Re: [PATCH v1 7/7] xen-block: implement indirect descriptors
On 09/04/13 20:49, Konrad Rzeszutek Wilk wrote:
> On Wed, Mar 27, 2013 at 12:10:43PM +0100, Roger Pau Monne wrote:
>> Indirect descriptors introduce a new block operation
>> (BLKIF_OP_INDIRECT) that passes grant references instead of segments
>> in the request. This grant references are filled with arrays of
>> blkif_request_segment_aligned, this way we can send more segments in a
>> request.
>>
>> The proposed implementation sets the maximum number of indirect grefs
>> (frames filled with blkif_request_segment_aligned) to 256 in the
>> backend and 32 in the frontend. The value in the frontend has been
>> chosen experimentally, and the backend value has been set to a sane
>> value that allows expanding the maximum number of indirect descriptors
>> in the frontend if needed.
>>
>> The migration code has changed from the previous implementation, in
>> which we simply remapped the segments on the shared ring. Now the
>> maximum number of segments allowed in a request can change depending
>> on the backend, so we have to requeue all the requests in the ring and
>> in the queue and split the bios in them if they are bigger than the
>> new maximum number of segments.
>>
>> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
>> Cc: xen-devel@...ts.xen.org
>> ---
>> drivers/block/xen-blkback/blkback.c | 136 +++++++---
>> drivers/block/xen-blkback/common.h | 82 ++++++-
>> drivers/block/xen-blkback/xenbus.c | 8 +
>> drivers/block/xen-blkfront.c | 490 +++++++++++++++++++++++++++++------
>> include/xen/interface/io/blkif.h | 26 ++
>> 5 files changed, 621 insertions(+), 121 deletions(-)
>>
>> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
>> index f8c838e..f16a7c9 100644
>> --- a/drivers/block/xen-blkback/blkback.c
>> +++ b/drivers/block/xen-blkback/blkback.c
>> @@ -69,7 +69,7 @@ MODULE_PARM_DESC(reqs, "Number of blkback requests to allocate per backend");
>> * IO workloads.
>> */
>>
>> -static int xen_blkif_max_buffer_pages = 704;
>> +static int xen_blkif_max_buffer_pages = 1024;
>> module_param_named(max_buffer_pages, xen_blkif_max_buffer_pages, int, 0644);
>> MODULE_PARM_DESC(max_buffer_pages,
>> "Maximum number of free pages to keep in each block backend buffer");
>> @@ -85,7 +85,7 @@ MODULE_PARM_DESC(max_buffer_pages,
>> * algorithm.
>> */
>>
>> -static int xen_blkif_max_pgrants = 352;
>> +static int xen_blkif_max_pgrants = 1056;
>> module_param_named(max_persistent_grants, xen_blkif_max_pgrants, int, 0644);
>> MODULE_PARM_DESC(max_persistent_grants,
>> "Maximum number of grants to map persistently");
>> @@ -631,10 +631,6 @@ purge_gnt_list:
>> return 0;
>> }
>>
>> -struct seg_buf {
>> - unsigned int offset;
>> - unsigned int nsec;
>> -};
>> /*
>> * Unmap the grant references, and also remove the M2P over-rides
>> * used in the 'pending_req'.
>> @@ -808,29 +804,71 @@ out_of_memory:
>> return -ENOMEM;
>> }
>>
>> -static int xen_blkbk_map_seg(struct blkif_request *req,
>> - struct pending_req *pending_req,
>> +static int xen_blkbk_map_seg(struct pending_req *pending_req,
>> struct seg_buf seg[],
>> struct page *pages[])
>> {
>> - int i, rc;
>> - grant_ref_t grefs[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> + int rc;
>>
>> - for (i = 0; i < req->u.rw.nr_segments; i++)
>> - grefs[i] = req->u.rw.seg[i].gref;
>> -
>> - rc = xen_blkbk_map(pending_req->blkif, grefs,
>> + rc = xen_blkbk_map(pending_req->blkif, pending_req->grefs,
>> pending_req->persistent_gnts,
>> pending_req->grant_handles, pending_req->pages,
>> - req->u.rw.nr_segments,
>> + pending_req->nr_pages,
>> (pending_req->operation != BLKIF_OP_READ));
>> - if (rc)
>> - return rc;
>>
>> - for (i = 0; i < req->u.rw.nr_segments; i++)
>> - seg[i].offset = (req->u.rw.seg[i].first_sect << 9);
>> + return rc;
>> +}
>>
>> - return 0;
>> +static int xen_blkbk_parse_indirect(struct blkif_request *req,
>> + struct pending_req *pending_req,
>> + struct seg_buf seg[],
>> + struct phys_req *preq)
>> +{
>> + struct persistent_gnt **persistent =
>> + pending_req->indirect_persistent_gnts;
>> + struct page **pages = pending_req->indirect_pages;
>> + struct xen_blkif *blkif = pending_req->blkif;
>> + int indirect_grefs, rc, n, nseg, i;
>> + struct blkif_request_segment_aligned *segments = NULL;
>> +
>> + nseg = pending_req->nr_pages;
>> + indirect_grefs = (nseg + SEGS_PER_INDIRECT_FRAME - 1) /
>> + SEGS_PER_INDIRECT_FRAME;
>
> Then 4096 + 511 / 511 = 8. OK. Looks good!
>
> Perhaps also have
> BUG_ON(indirect_grefs > BLKIF_MAX_INDIRECT_PAGES_PER_REQUEST);
>
> just in case?
Since we already have a check for the number of segments in
dispatch_rw_block_io:
unlikely((req->operation == BLKIF_OP_INDIRECT) &&
(nseg > MAX_INDIRECT_SEGMENTS)))
Adding a BUG should be safe.
>
>> +
>> + rc = xen_blkbk_map(blkif, req->u.indirect.indirect_grefs,
>> + persistent, pending_req->indirect_handles,
>> + pages, indirect_grefs, true);
>> + if (rc)
>> + goto unmap;
>> +
>> + for (n = 0, i = 0; n < nseg; n++) {
>> + if ((n % SEGS_PER_INDIRECT_FRAME) == 0) {
>> + /* Map indirect segments */
>> + if (segments)
>> + kunmap_atomic(segments);
>> + segments =
>> + kmap_atomic(pages[n/SEGS_PER_INDIRECT_FRAME]);
>
> You can make it in one-line.
>
>
>> + }
>> + i = n % SEGS_PER_INDIRECT_FRAME;
>> + pending_req->grefs[n] = segments[i].gref;
>> + seg[n].nsec = segments[i].last_sect -
>> + segments[i].first_sect + 1;
>> + seg[n].offset = (segments[i].first_sect << 9);
>> + if ((segments[i].last_sect >= (PAGE_SIZE >> 9)) ||
>> + (segments[i].last_sect <
>> + segments[i].first_sect)) {
>> + rc = -EINVAL;
>> + goto unmap;
>> + }
>> + preq->nr_sects += seg[n].nsec;
>> + }
>> +
>> +unmap:
>> + if (segments)
>> + kunmap_atomic(segments);
>> + xen_blkbk_unmap(blkif, pending_req->indirect_handles,
>> + pages, persistent, indirect_grefs);
>> + return rc;
>> }
>>
>> static int dispatch_discard_io(struct xen_blkif *blkif,
>> @@ -1003,6 +1041,7 @@ __do_block_io_op(struct xen_blkif *blkif)
>> case BLKIF_OP_WRITE:
>> case BLKIF_OP_WRITE_BARRIER:
>> case BLKIF_OP_FLUSH_DISKCACHE:
>> + case BLKIF_OP_INDIRECT:
>> if (dispatch_rw_block_io(blkif, &req, pending_req))
>> goto done;
>> break;
>> @@ -1049,17 +1088,28 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>> struct pending_req *pending_req)
>> {
>> struct phys_req preq;
>> - struct seg_buf seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> + struct seg_buf *seg = pending_req->seg;
>> unsigned int nseg;
>> struct bio *bio = NULL;
>> - struct bio *biolist[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> + struct bio **biolist = pending_req->biolist;
>> int i, nbio = 0;
>> int operation;
>> struct blk_plug plug;
>> bool drain = false;
>> struct page **pages = pending_req->pages;
>> + unsigned short req_operation;
>> +
>> + req_operation = req->operation == BLKIF_OP_INDIRECT ?
>> + req->u.indirect.indirect_op : req->operation;
>> + if ((req->operation == BLKIF_OP_INDIRECT) &&
>> + (req_operation != BLKIF_OP_READ) &&
>> + (req_operation != BLKIF_OP_WRITE)) {
>> + pr_debug(DRV_PFX "Invalid indirect operation (%u)\n",
>> + req_operation);
>> + goto fail_response;
>> + }
>>
>> - switch (req->operation) {
>> + switch (req_operation) {
>> case BLKIF_OP_READ:
>> blkif->st_rd_req++;
>> operation = READ;
>> @@ -1081,33 +1131,47 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>> }
>>
>> /* Check that the number of segments is sane. */
>> - nseg = req->u.rw.nr_segments;
>> + nseg = req->operation == BLKIF_OP_INDIRECT ?
>> + req->u.indirect.nr_segments : req->u.rw.nr_segments;
>>
>> if (unlikely(nseg == 0 && operation != WRITE_FLUSH) ||
>> - unlikely(nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) {
>> + unlikely((req->operation != BLKIF_OP_INDIRECT) &&
>> + (nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) ||
>> + unlikely((req->operation == BLKIF_OP_INDIRECT) &&
>> + (nseg > MAX_INDIRECT_SEGMENTS))) {
>> pr_debug(DRV_PFX "Bad number of segments in request (%d)\n",
>> nseg);
>> /* Haven't submitted any bio's yet. */
>> goto fail_response;
>> }
>>
>> - preq.sector_number = req->u.rw.sector_number;
>> preq.nr_sects = 0;
>>
>> pending_req->blkif = blkif;
>> pending_req->id = req->u.rw.id;
>> - pending_req->operation = req->operation;
>> + pending_req->operation = req_operation;
>> pending_req->status = BLKIF_RSP_OKAY;
>> pending_req->nr_pages = nseg;
>>
>> - for (i = 0; i < nseg; i++) {
>> - seg[i].nsec = req->u.rw.seg[i].last_sect -
>> - req->u.rw.seg[i].first_sect + 1;
>> - if ((req->u.rw.seg[i].last_sect >= (PAGE_SIZE >> 9)) ||
>> - (req->u.rw.seg[i].last_sect < req->u.rw.seg[i].first_sect))
>> + if (req->operation != BLKIF_OP_INDIRECT) {
>> + preq.dev = req->u.rw.handle;
>> + preq.sector_number = req->u.rw.sector_number;
>> + for (i = 0; i < nseg; i++) {
>> + pending_req->grefs[i] = req->u.rw.seg[i].gref;
>> + seg[i].nsec = req->u.rw.seg[i].last_sect -
>> + req->u.rw.seg[i].first_sect + 1;
>> + seg[i].offset = (req->u.rw.seg[i].first_sect << 9);
>> + if ((req->u.rw.seg[i].last_sect >= (PAGE_SIZE >> 9)) ||
>> + (req->u.rw.seg[i].last_sect <
>> + req->u.rw.seg[i].first_sect))
>> + goto fail_response;
>> + preq.nr_sects += seg[i].nsec;
>> + }
>> + } else {
>> + preq.dev = req->u.indirect.handle;
>> + preq.sector_number = req->u.indirect.sector_number;
>> + if (xen_blkbk_parse_indirect(req, pending_req, seg, &preq))
>> goto fail_response;
>> - preq.nr_sects += seg[i].nsec;
>> -
>> }
>>
>> if (xen_vbd_translate(&preq, blkif, operation) != 0) {
>> @@ -1144,7 +1208,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>> * the hypercall to unmap the grants - that is all done in
>> * xen_blkbk_unmap.
>> */
>> - if (xen_blkbk_map_seg(req, pending_req, seg, pages))
>> + if (xen_blkbk_map_seg(pending_req, seg, pages))
>> goto fail_flush;
>>
>> /*
>> @@ -1210,7 +1274,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>> pending_req->nr_pages);
>> fail_response:
>> /* Haven't submitted any bio's yet. */
>> - make_response(blkif, req->u.rw.id, req->operation, BLKIF_RSP_ERROR);
>> + make_response(blkif, req->u.rw.id, req_operation, BLKIF_RSP_ERROR);
>> free_req(blkif, pending_req);
>> msleep(1); /* back off a bit */
>> return -EIO;
>> diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
>> index debff44..30bffcc 100644
>> --- a/drivers/block/xen-blkback/common.h
>> +++ b/drivers/block/xen-blkback/common.h
>> @@ -50,6 +50,17 @@
>> __func__, __LINE__, ##args)
>>
>>
>> +/*
>> + * This is the maximum number of segments that would be allowed in indirect
>> + * requests. This value will also be passed to the frontend.
>> + */
>> +#define MAX_INDIRECT_SEGMENTS 256
>
> That little? We don't want to have say 512 to at least fill the full page? Or
> perhaps 1024 to use two pages (and be able to comfortably do 4MB of I/O in
> one request).
Yes, we can set this to a different value, but what really matters is
the value used in blkfront.
Also, from what I've found, setting this to a higher value only improves
performance if the maximum number of persistent grants is also
increased. For example allowing requests with 512 segments and only
using 1056 persistent grants (so we are only persistently mapping 7% of
all the possible grants) will be a performance degradation in comparison
to using only 32 segments per request and 1056 persistent grants (100%
of the grants mapped persistently).
>
>> +
>> +#define SEGS_PER_INDIRECT_FRAME \
>> +(PAGE_SIZE/sizeof(struct blkif_request_segment_aligned))
>
> OK, so 512.
>
>> +#define MAX_INDIRECT_GREFS \
>> +((MAX_INDIRECT_SEGMENTS + SEGS_PER_INDIRECT_FRAME - 1)/SEGS_PER_INDIRECT_FRAME)
>
>
> (256 + 512 - 1) / 512 = so 1.49 or since it is an int = '1'.
>
> Is that right? The patch comment alluded to 256?
>
> Ah, MAX_INDIRECT_GREFS is how many pages of indirect descriptors we can do!
> Somehow I thought it was related to how many indirect grant references we
> have (so SEGS_PER_INDIRECT_FRAME).
>
> How about just calling it MAX_INDIRECT_PAGES ?
Yes, that's a better name.
>
> This should also have some
>
> BUILD_BUG_ON(MAX_INDIRECT_GREFS > BLKIF_MAX_INDIRECT_PAGES_PER_REQUEST)
>
> to guard against doing something very bad.
>
>
>> +
>> /* Not a real protocol. Used to generate ring structs which contain
>> * the elements common to all protocols only. This way we get a
>> * compiler-checkable way to use common struct elements, so we can
>> @@ -83,12 +94,23 @@ struct blkif_x86_32_request_other {
>> uint64_t id; /* private guest value, echoed in resp */
>> } __attribute__((__packed__));
>>
>> +struct blkif_x86_32_request_indirect {
>> + uint8_t indirect_op;
>> + uint16_t nr_segments;
>
> This needs to be documented. Is there are limit to what it can be? What if
> the frontend sets it to 1231231?
This is checked in dispatch_rw_block_io:
if (unlikely(nseg == 0 && operation != WRITE_FLUSH) ||
unlikely((req->operation != BLKIF_OP_INDIRECT) &&
(nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) ||
unlikely((req->operation == BLKIF_OP_INDIRECT) &&
(nseg > MAX_INDIRECT_SEGMENTS))) {
pr_debug(DRV_PFX "Bad number of segments in request (%d)\n",
nseg);
/* Haven't submitted any bio's yet. */
goto fail_response;
}
And the value of MAX_INDIRECT_SEGMENTS is exported to the frontend in
xenstore, so the frontend does:
max_indirect_segments = min(MAX_INDIRECT_SEGMENTS, front_max_segments);
To know how many segments it can safely use in an indirect op.
>
>> + uint64_t id;
>> + blkif_sector_t sector_number;
>> + blkif_vdev_t handle;
>> + uint16_t _pad1;
>> + grant_ref_t indirect_grefs[BLKIF_MAX_INDIRECT_GREFS_PER_REQUEST];
>
> And how do we figure out whether we are going to use one indirect_grefs or many?
> That should be described here. (if I understand it right it would be done
> via the maximum-indirect-something' variable)
I've added the following comment:
/*
* The maximum number of indirect segments (and pages) that will
* be used is determined by MAX_INDIRECT_SEGMENTS, this value
* is also exported to the guest (via xenstore max-indirect-segments
* entry), so the frontend knows how many indirect segments the
* backend supports.
*/
>
>
>> +} __attribute__((__packed__));
>> +
>
> Per my calculation the size of this structure is 55 bytes. The 64-bit is 59 bytes.
>
> It is a bit odd, but then 1 byte is for the 'operation' in the 'blkif_x*_request',
> so it comes out to 56 and 60 bytes.
>
> Is that still the right amount ? I thought we wanted to flesh it out to be a nice
> 64 byte aligned so that the future patches which will make the requests be
> more cache-aligned and won't have to play games?
Yes, I've added a uint32_t for 64bits and a uint64_t for 32bits, that
makes it 64bytes aligned in both cases.
>
>> struct blkif_x86_32_request {
>> uint8_t operation; /* BLKIF_OP_??? */
>> union {
>> struct blkif_x86_32_request_rw rw;
>> struct blkif_x86_32_request_discard discard;
>> struct blkif_x86_32_request_other other;
>> + struct blkif_x86_32_request_indirect indirect;
>> } u;
>> } __attribute__((__packed__));
>>
>> @@ -127,12 +149,24 @@ struct blkif_x86_64_request_other {
>> uint64_t id; /* private guest value, echoed in resp */
>> } __attribute__((__packed__));
>>
>> +struct blkif_x86_64_request_indirect {
>> + uint8_t indirect_op;
>> + uint16_t nr_segments;
>> + uint32_t _pad1; /* offsetof(blkif_..,u.indirect.id)==8 */
>
> The comment is a bit off compared to the rest.
>
>> + uint64_t id;
>> + blkif_sector_t sector_number;
>> + blkif_vdev_t handle;
>> + uint16_t _pad2;
>> + grant_ref_t indirect_grefs[BLKIF_MAX_INDIRECT_GREFS_PER_REQUEST];
>> +} __attribute__((__packed__));
>> +
>> struct blkif_x86_64_request {
>> uint8_t operation; /* BLKIF_OP_??? */
>> union {
>> struct blkif_x86_64_request_rw rw;
>> struct blkif_x86_64_request_discard discard;
>> struct blkif_x86_64_request_other other;
>> + struct blkif_x86_64_request_indirect indirect;
>> } u;
>> } __attribute__((__packed__));
>>
>> @@ -257,6 +291,11 @@ struct xen_blkif {
>> wait_queue_head_t waiting_to_free;
>> };
>>
>> +struct seg_buf {
>> + unsigned long offset;
>> + unsigned int nsec;
>> +};
>> +
>> /*
>> * Each outstanding request that we've passed to the lower device layers has a
>> * 'pending_req' allocated to it. Each buffer_head that completes decrements
>> @@ -271,9 +310,16 @@ struct pending_req {
>> unsigned short operation;
>> int status;
>> struct list_head free_list;
>> - struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> - struct persistent_gnt *persistent_gnts[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> - grant_handle_t grant_handles[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> + struct page *pages[MAX_INDIRECT_SEGMENTS];
>> + struct persistent_gnt *persistent_gnts[MAX_INDIRECT_SEGMENTS];
>> + grant_handle_t grant_handles[MAX_INDIRECT_SEGMENTS];
>> + grant_ref_t grefs[MAX_INDIRECT_SEGMENTS];
>> + /* Indirect descriptors */
>> + struct persistent_gnt *indirect_persistent_gnts[MAX_INDIRECT_GREFS];
>> + struct page *indirect_pages[MAX_INDIRECT_GREFS];
>> + grant_handle_t indirect_handles[MAX_INDIRECT_GREFS];
>> + struct seg_buf seg[MAX_INDIRECT_SEGMENTS];
>> + struct bio *biolist[MAX_INDIRECT_SEGMENTS];
>
> Oh wow. That is a big structure. So 1536 for the BLKIF_MAX_SEGMENTS_PER_REQUEST
> ones and 24 bytes for the ones that deail with MAX_INDIRECT_GREFS.
>
> This could be made look nicer. For example you could do:
>
> struct indirect {
> struct page;
> grant_handle_t handle;
> struct persistent_gnt *gnt;
> } desc[MAX_INDIRECT_GREFS];
>
> .. and the same treatment to the BLKIF_MAX_SEGMENTS_PER_REQUEST
> one.
>
> Thought perhaps it makes more sense to do that with a later patch as a cleanup.
This was similar to what Jan was suggesting, but I would prefer to leave
that for a latter patch.
>> };
>>
>>
>> @@ -312,7 +358,7 @@ struct xenbus_device *xen_blkbk_xenbus(struct backend_info *be);
>> static inline void blkif_get_x86_32_req(struct blkif_request *dst,
>> struct blkif_x86_32_request *src)
>> {
>> - int i, n = BLKIF_MAX_SEGMENTS_PER_REQUEST;
>> + int i, n = BLKIF_MAX_SEGMENTS_PER_REQUEST, j = MAX_INDIRECT_GREFS;
>> dst->operation = src->operation;
>> switch (src->operation) {
>> case BLKIF_OP_READ:
>> @@ -335,6 +381,19 @@ static inline void blkif_get_x86_32_req(struct blkif_request *dst,
>> dst->u.discard.sector_number = src->u.discard.sector_number;
>> dst->u.discard.nr_sectors = src->u.discard.nr_sectors;
>> break;
>> + case BLKIF_OP_INDIRECT:
>> + dst->u.indirect.indirect_op = src->u.indirect.indirect_op;
>> + dst->u.indirect.nr_segments = src->u.indirect.nr_segments;
>> + dst->u.indirect.handle = src->u.indirect.handle;
>> + dst->u.indirect.id = src->u.indirect.id;
>> + dst->u.indirect.sector_number = src->u.indirect.sector_number;
>> + barrier();
>> + if (j > dst->u.indirect.nr_segments)
>> + j = dst->u.indirect.nr_segments;
>
> How about just:
> j = min(MAX_INDIRECT_GREFS, dst->u.indirect.nr_segments);
>
> But.. you are using the 'nr_segments' and 'j' (which is 1) which is odd. j ends up
> being set to 1. But you are somehow mixing 'nr_segments' and 'MAX_INDIRECT_GREFS'
> which is confusing. Perhaps you meant:
>
> if (j > min(dst->u.inderect.nr_segments, SEGS_PER_INDIRECT_FRAME) / SEGS_PER_INDIRECT_FRAME)
> ...
>
> After all, the 'j' is suppose to tell you how many indirect pages to use, and that
> should be driven by the total amount of nr_segments.
>
> Thought if nr_segments is absuredly high we should detect that and do something
> about it.
This is indeed not right, I've added a macro to calculate the number of
indirect pages based on the number of segments, so now if looks like:
j = min(MAX_INDIRECT_PAGES,
INDIRECT_PAGES(dst->u.indirect.nr_segments));
>
>> + for (i = 0; i < j; i++)
>> + dst->u.indirect.indirect_grefs[i] =
>> + src->u.indirect.indirect_grefs[i];
>> + break;
>> default:
>> /*
>> * Don't know how to translate this op. Only get the
>> @@ -348,7 +407,7 @@ static inline void blkif_get_x86_32_req(struct blkif_request *dst,
>> static inline void blkif_get_x86_64_req(struct blkif_request *dst,
>> struct blkif_x86_64_request *src)
>> {
>> - int i, n = BLKIF_MAX_SEGMENTS_PER_REQUEST;
>> + int i, n = BLKIF_MAX_SEGMENTS_PER_REQUEST, j = MAX_INDIRECT_GREFS;
>> dst->operation = src->operation;
>> switch (src->operation) {
>> case BLKIF_OP_READ:
>> @@ -371,6 +430,19 @@ static inline void blkif_get_x86_64_req(struct blkif_request *dst,
>> dst->u.discard.sector_number = src->u.discard.sector_number;
>> dst->u.discard.nr_sectors = src->u.discard.nr_sectors;
>> break;
>> + case BLKIF_OP_INDIRECT:
>> + dst->u.indirect.indirect_op = src->u.indirect.indirect_op;
>> + dst->u.indirect.nr_segments = src->u.indirect.nr_segments;
>> + dst->u.indirect.handle = src->u.indirect.handle;
>> + dst->u.indirect.id = src->u.indirect.id;
>> + dst->u.indirect.sector_number = src->u.indirect.sector_number;
>> + barrier();
>> + if (j > dst->u.indirect.nr_segments)
>> + j = dst->u.indirect.nr_segments;
>
> Same here. The min is a nice macro.
Done.
>> + for (i = 0; i < j; i++)
>> + dst->u.indirect.indirect_grefs[i] =
>> + src->u.indirect.indirect_grefs[i];
>> + break;
>> default:
>> /*
>> * Don't know how to translate this op. Only get the
>> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
>> index bf7344f..172cf89 100644
>> --- a/drivers/block/xen-blkback/xenbus.c
>> +++ b/drivers/block/xen-blkback/xenbus.c
>> @@ -703,6 +703,14 @@ again:
>> goto abort;
>> }
>>
>> + err = xenbus_printf(xbt, dev->nodename, "max-indirect-segments", "%u",
>> + MAX_INDIRECT_SEGMENTS);
>
> Ahem. That should be 'feature-max-indirect-segments'.
Done, replaced all occurences of 'max-indirect-segments' with
'feature-max-indirect-segments'.
>
>> + if (err) {
>> + xenbus_dev_fatal(dev, err, "writing %s/max-indirect-segments",
>> + dev->nodename);
>> + goto abort;
>
> That is not fatal. We can continue on without having that enabled.
OK, removed the abort.
>
>> + }
>> +
>> err = xenbus_printf(xbt, dev->nodename, "sectors", "%llu",
>> (unsigned long long)vbd_sz(&be->blkif->vbd));
>> if (err) {
>> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
>> index a894f88..ecbc26a 100644
>> --- a/drivers/block/xen-blkfront.c
>> +++ b/drivers/block/xen-blkfront.c
>> @@ -74,12 +74,30 @@ struct grant {
>> struct blk_shadow {
>> struct blkif_request req;
>> struct request *request;
>> - struct grant *grants_used[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> + struct grant **grants_used;
>> + struct grant **indirect_grants;
>> +};
>> +
>> +struct split_bio {
>> + struct bio *bio;
>> + atomic_t pending;
>> + int err;
>> };
>>
>> static DEFINE_MUTEX(blkfront_mutex);
>> static const struct block_device_operations xlvbd_block_fops;
>>
>> +/*
>> + * Maximum number of segments in indirect requests, the actual value used by
>> + * the frontend driver is the minimum of this value and the value provided
>> + * by the backend driver.
>> + */
>> +
>> +static int xen_blkif_max_segments = 32;
>> +module_param_named(max_segments, xen_blkif_max_segments, int, 0);
>> +MODULE_PARM_DESC(max_segments,
>> +"Maximum number of segments in indirect requests");
>
> This means a new entry in Documentation/ABI/sysfs/...
I think I should just not allow this to be exported, since we cannot
change it at run-time, so if a user changes the 0 to something else, and
changes the value... nothing will happen (because this is only used
before the device is connected).
>
> Perhaps the xen-blkfront part of the patch should be just split out to make
> this easier?
>
> Perhaps what we really should have is just the 'max' value of megabytes
> we want to handle on the ring.
>
> As right now 32 ring requests * 32 segments = 4MB. But if the user wants
> to se the max: 32 * 4096 = so 512MB (right? each request would handle now 16MB
> and since we have 32 of them = 512MB).
I've just set that to something that brings a performance benefit
without having to map an insane number of persistent grants in blkback.
Yes, the values are correct, but the device request queue (rq) is only
able to provide read requests with 64 segments or write requests with
128 segments. I haven't been able to get larger requests, even when
setting this to 512 or higer.
>
>> +
>> #define BLK_RING_SIZE __CONST_RING_SIZE(blkif, PAGE_SIZE)
>>
>> /*
>> @@ -98,7 +116,7 @@ struct blkfront_info
>> enum blkif_state connected;
>> int ring_ref;
>> struct blkif_front_ring ring;
>> - struct scatterlist sg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> + struct scatterlist *sg;
>> unsigned int evtchn, irq;
>> struct request_queue *rq;
>> struct work_struct work;
>> @@ -114,6 +132,8 @@ struct blkfront_info
>> unsigned int discard_granularity;
>> unsigned int discard_alignment;
>> unsigned int feature_persistent:1;
>> + unsigned int max_indirect_segments;
>> + unsigned int sector_size;
>
> sector_size? That looks like it belongs to a different patch?
Yes, this sector_size clearly doesn't belong here.
>> int is_ready;
>> };
>>
>> @@ -142,6 +162,14 @@ static DEFINE_SPINLOCK(minor_lock);
>>
>> #define DEV_NAME "xvd" /* name in /dev */
>>
>> +#define SEGS_PER_INDIRECT_FRAME \
>> + (PAGE_SIZE/sizeof(struct blkif_request_segment_aligned))
>> +#define INDIRECT_GREFS(_segs) \
>> + ((_segs + SEGS_PER_INDIRECT_FRAME - 1)/SEGS_PER_INDIRECT_FRAME)
>> +#define MIN(_a, _b) ((_a) < (_b) ? (_a) : (_b))
>
> No need. Just use 'min'
>
>> +
>> +static int blkfront_setup_indirect(struct blkfront_info *info);
>> +
>> static int get_id_from_freelist(struct blkfront_info *info)
>> {
>> unsigned long free = info->shadow_free;
>> @@ -358,7 +386,8 @@ static int blkif_queue_request(struct request *req)
>> struct blkif_request *ring_req;
>> unsigned long id;
>> unsigned int fsect, lsect;
>> - int i, ref;
>> + int i, ref, n;
>> + struct blkif_request_segment_aligned *segments = NULL;
>>
>> /*
>> * Used to store if we are able to queue the request by just using
>> @@ -369,21 +398,27 @@ static int blkif_queue_request(struct request *req)
>> grant_ref_t gref_head;
>> struct grant *gnt_list_entry = NULL;
>> struct scatterlist *sg;
>> + int nseg, max_grefs;
>>
>> if (unlikely(info->connected != BLKIF_STATE_CONNECTED))
>> return 1;
>>
>> - /* Check if we have enought grants to allocate a requests */
>> - if (info->persistent_gnts_c < BLKIF_MAX_SEGMENTS_PER_REQUEST) {
>> + max_grefs = info->max_indirect_segments ?
>> + info->max_indirect_segments +
>> + INDIRECT_GREFS(info->max_indirect_segments) :
>> + BLKIF_MAX_SEGMENTS_PER_REQUEST;
>> +
>> + /* Check if we have enough grants to allocate a requests */
>> + if (info->persistent_gnts_c < max_grefs) {
>> new_persistent_gnts = 1;
>> if (gnttab_alloc_grant_references(
>> - BLKIF_MAX_SEGMENTS_PER_REQUEST - info->persistent_gnts_c,
>> + max_grefs - info->persistent_gnts_c,
>> &gref_head) < 0) {
>> gnttab_request_free_callback(
>> &info->callback,
>> blkif_restart_queue_callback,
>> info,
>> - BLKIF_MAX_SEGMENTS_PER_REQUEST);
>> + max_grefs);
>> return 1;
>> }
>> } else
>> @@ -394,42 +429,74 @@ static int blkif_queue_request(struct request *req)
>> id = get_id_from_freelist(info);
>> info->shadow[id].request = req;
>>
>> - ring_req->u.rw.id = id;
>> - ring_req->u.rw.sector_number = (blkif_sector_t)blk_rq_pos(req);
>> - ring_req->u.rw.handle = info->handle;
>> -
>> - ring_req->operation = rq_data_dir(req) ?
>> - BLKIF_OP_WRITE : BLKIF_OP_READ;
>> -
>> - if (req->cmd_flags & (REQ_FLUSH | REQ_FUA)) {
>> - /*
>> - * Ideally we can do an unordered flush-to-disk. In case the
>> - * backend onlysupports barriers, use that. A barrier request
>> - * a superset of FUA, so we can implement it the same
>> - * way. (It's also a FLUSH+FUA, since it is
>> - * guaranteed ordered WRT previous writes.)
>> - */
>> - ring_req->operation = info->flush_op;
>> - }
>> -
>> if (unlikely(req->cmd_flags & (REQ_DISCARD | REQ_SECURE))) {
>> /* id, sector_number and handle are set above. */
>
> And you can also remove that comment or change it and mention that we don't
> care about the 'handle' value.
>> ring_req->operation = BLKIF_OP_DISCARD;
>> ring_req->u.discard.nr_sectors = blk_rq_sectors(req);
>> + ring_req->u.discard.id = id;
>> + ring_req->u.discard.sector_number =
>> + (blkif_sector_t)blk_rq_pos(req);
>
> One line pls.
Both comments fixed.
>
>
>> if ((req->cmd_flags & REQ_SECURE) && info->feature_secdiscard)
>> ring_req->u.discard.flag = BLKIF_DISCARD_SECURE;
>> else
>> ring_req->u.discard.flag = 0;
>> } else {
>> - ring_req->u.rw.nr_segments = blk_rq_map_sg(req->q, req,
>> - info->sg);
>> - BUG_ON(ring_req->u.rw.nr_segments >
>> - BLKIF_MAX_SEGMENTS_PER_REQUEST);
>> -
>> - for_each_sg(info->sg, sg, ring_req->u.rw.nr_segments, i) {
>> + BUG_ON(info->max_indirect_segments == 0 &&
>> + req->nr_phys_segments > BLKIF_MAX_SEGMENTS_PER_REQUEST);
>> + BUG_ON(info->max_indirect_segments &&
>> + req->nr_phys_segments > info->max_indirect_segments);
>> + nseg = blk_rq_map_sg(req->q, req, info->sg);
>> + ring_req->u.rw.id = id;
>> + if (nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST) {
>> + /*
>> + * The indirect operation can only be a BLKIF_OP_READ or
>> + * BLKIF_OP_WRITE
>> + */
>> + BUG_ON(req->cmd_flags & (REQ_FLUSH | REQ_FUA));
>> + ring_req->operation = BLKIF_OP_INDIRECT;
>> + ring_req->u.indirect.indirect_op = rq_data_dir(req) ?
>> + BLKIF_OP_WRITE : BLKIF_OP_READ;
>> + ring_req->u.indirect.sector_number =
>> + (blkif_sector_t)blk_rq_pos(req);
>> + ring_req->u.indirect.handle = info->handle;
>> + ring_req->u.indirect.nr_segments = nseg;
>> + } else {
>> + ring_req->u.rw.sector_number =
>> + (blkif_sector_t)blk_rq_pos(req);
>> + ring_req->u.rw.handle = info->handle;
>> + ring_req->operation = rq_data_dir(req) ?
>> + BLKIF_OP_WRITE : BLKIF_OP_READ;
>> + if (req->cmd_flags & (REQ_FLUSH | REQ_FUA)) {
>> + /*
>> + * Ideally we can do an unordered flush-to-disk. In case the
>> + * backend onlysupports barriers, use that. A barrier request
>> + * a superset of FUA, so we can implement it the same
>> + * way. (It's also a FLUSH+FUA, since it is
>> + * guaranteed ordered WRT previous writes.)
>> + */
>
>
> Something is off with that comment.
Yes, because I just moved the comment around, I didn't want to change
it, so I indented it differently to fit within 80 cols, now that I know
we can use longer lines I will align it normally.
>> + ring_req->operation = info->flush_op;
>> + }
>> + ring_req->u.rw.nr_segments = nseg;
>> + }
>> + for_each_sg(info->sg, sg, nseg, i) {
>> fsect = sg->offset >> 9;
>> lsect = fsect + (sg->length >> 9) - 1;
>>
>> + if ((ring_req->operation == BLKIF_OP_INDIRECT) &&
>> + (i % SEGS_PER_INDIRECT_FRAME == 0)) {
>> + if (segments)
>> + kunmap_atomic(segments);
>> +
>> + n = i / SEGS_PER_INDIRECT_FRAME;
>> + gnt_list_entry = get_grant(&gref_head, info);
>> + info->shadow[id].indirect_grants[n] =
>> + gnt_list_entry;
>
> One line pls
>> + segments = kmap_atomic(
>> + pfn_to_page(gnt_list_entry->pfn));
>
> Ditto
>> + ring_req->u.indirect.indirect_grefs[n] =
>> + gnt_list_entry->gref;
>
> Ditto.
I've fixed this, and some that were a couple of lines up.
>> + }
>> +
>> gnt_list_entry = get_grant(&gref_head, info);
>> ref = gnt_list_entry->gref;
>>
>> @@ -461,13 +528,23 @@ static int blkif_queue_request(struct request *req)
>> kunmap_atomic(bvec_data);
>> kunmap_atomic(shared_data);
>> }
>> -
>> - ring_req->u.rw.seg[i] =
>> - (struct blkif_request_segment) {
>> - .gref = ref,
>> - .first_sect = fsect,
>> - .last_sect = lsect };
>> + if (ring_req->operation != BLKIF_OP_INDIRECT) {
>> + ring_req->u.rw.seg[i] =
>> + (struct blkif_request_segment) {
>> + .gref = ref,
>> + .first_sect = fsect,
>> + .last_sect = lsect };
>> + } else {
>> + n = i % SEGS_PER_INDIRECT_FRAME;
>> + segments[n] =
>> + (struct blkif_request_segment_aligned) {
>> + .gref = ref,
>> + .first_sect = fsect,
>> + .last_sect = lsect };
>> + }
>> }
>> + if (segments)
>> + kunmap_atomic(segments);
>> }
>>
>> info->ring.req_prod_pvt++;
>> @@ -542,7 +619,8 @@ wait:
>> flush_requests(info);
>> }
>>
>> -static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size)
>> +static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
>> + unsigned int segments)
>> {
>> struct request_queue *rq;
>> struct blkfront_info *info = gd->private_data;
>> @@ -571,7 +649,7 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size)
>> blk_queue_max_segment_size(rq, PAGE_SIZE);
>>
>> /* Ensure a merged request will fit in a single I/O ring slot. */
>> - blk_queue_max_segments(rq, BLKIF_MAX_SEGMENTS_PER_REQUEST);
>> + blk_queue_max_segments(rq, segments);
>>
>> /* Make sure buffer addresses are sector-aligned. */
>> blk_queue_dma_alignment(rq, 511);
>> @@ -588,13 +666,14 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size)
>> static void xlvbd_flush(struct blkfront_info *info)
>> {
>> blk_queue_flush(info->rq, info->feature_flush);
>> - printk(KERN_INFO "blkfront: %s: %s: %s %s\n",
>> + printk(KERN_INFO "blkfront: %s: %s: %s %s %s\n",
>> info->gd->disk_name,
>> info->flush_op == BLKIF_OP_WRITE_BARRIER ?
>> "barrier" : (info->flush_op == BLKIF_OP_FLUSH_DISKCACHE ?
>> "flush diskcache" : "barrier or flush"),
>> info->feature_flush ? "enabled" : "disabled",
>> - info->feature_persistent ? "using persistent grants" : "");
>> + info->feature_persistent ? "using persistent grants" : "",
>> + info->max_indirect_segments ? "using indirect descriptors" : "");
>
> This is a bit of mess now:
>
>
> [ 0.968241] blkfront: xvda: barrier or flush: disabled using persistent grants using indirect descriptors
>
> Should it just be:
>
> 'persistent_grants: enabled; indirect descriptors: enabled'
>
> ?
Agreed. If you don't mind I will change the wording for both persistent
grants and indirect descriptors in this same patch.
>> }
>>
>> static int xen_translate_vdev(int vdevice, int *minor, unsigned int *offset)
>> @@ -734,7 +813,9 @@ static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
>> gd->driverfs_dev = &(info->xbdev->dev);
>> set_capacity(gd, capacity);
>>
>> - if (xlvbd_init_blk_queue(gd, sector_size)) {
>> + if (xlvbd_init_blk_queue(gd, sector_size,
>> + info->max_indirect_segments ? :
>> + BLKIF_MAX_SEGMENTS_PER_REQUEST)) {
>> del_gendisk(gd);
>> goto release;
>> }
>> @@ -818,6 +899,7 @@ static void blkif_free(struct blkfront_info *info, int suspend)
>> {
>> struct grant *persistent_gnt;
>> struct grant *n;
>> + int i, j, segs;
>>
>> /* Prevent new requests being issued until we fix things up. */
>> spin_lock_irq(&info->io_lock);
>> @@ -843,6 +925,47 @@ static void blkif_free(struct blkfront_info *info, int suspend)
>> }
>> BUG_ON(info->persistent_gnts_c != 0);
>>
>> + kfree(info->sg);
>> + info->sg = NULL;
>> + for (i = 0; i < BLK_RING_SIZE; i++) {
>> + /*
>> + * Clear persistent grants present in requests already
>> + * on the shared ring
>> + */
>> + if (!info->shadow[i].request)
>> + goto free_shadow;
>> +
>> + segs = info->shadow[i].req.operation == BLKIF_OP_INDIRECT ?
>> + info->shadow[i].req.u.indirect.nr_segments :
>> + info->shadow[i].req.u.rw.nr_segments;
>> + for (j = 0; j < segs; j++) {
>> + persistent_gnt = info->shadow[i].grants_used[j];
>> + gnttab_end_foreign_access(persistent_gnt->gref, 0, 0UL);
>> + __free_page(pfn_to_page(persistent_gnt->pfn));
>> + kfree(persistent_gnt);
>> + }
>> +
>> + if (info->shadow[i].req.operation != BLKIF_OP_INDIRECT)
>> + /*
>> + * If this is not an indirect operation don't try to
>> + * free indirect segments
>> + */
>> + goto free_shadow;
>> +
>> + for (j = 0; j < INDIRECT_GREFS(segs); j++) {
>> + persistent_gnt = info->shadow[i].indirect_grants[j];
>> + gnttab_end_foreign_access(persistent_gnt->gref, 0, 0UL);
>> + __free_page(pfn_to_page(persistent_gnt->pfn));
>> + kfree(persistent_gnt);
>> + }
>> +
>> +free_shadow:
>> + kfree(info->shadow[i].grants_used);
>> + info->shadow[i].grants_used = NULL;
>> + kfree(info->shadow[i].indirect_grants);
>> + info->shadow[i].indirect_grants = NULL;
>> + }
>> +
>> /* No more gnttab callback work. */
>> gnttab_cancel_free_callback(&info->callback);
>> spin_unlock_irq(&info->io_lock);
>> @@ -873,6 +996,10 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
>> char *bvec_data;
>> void *shared_data;
>> unsigned int offset = 0;
>> + int nseg;
>> +
>> + nseg = s->req.operation == BLKIF_OP_INDIRECT ?
>> + s->req.u.indirect.nr_segments : s->req.u.rw.nr_segments;
>>
>> if (bret->operation == BLKIF_OP_READ) {
>> /*
>> @@ -885,7 +1012,7 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
>> BUG_ON((bvec->bv_offset + bvec->bv_len) > PAGE_SIZE);
>> if (bvec->bv_offset < offset)
>> i++;
>> - BUG_ON(i >= s->req.u.rw.nr_segments);
>> + BUG_ON(i >= nseg);
>> shared_data = kmap_atomic(
>> pfn_to_page(s->grants_used[i]->pfn));
>> bvec_data = bvec_kmap_irq(bvec, &flags);
>> @@ -897,10 +1024,17 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
>> }
>> }
>> /* Add the persistent grant into the list of free grants */
>> - for (i = 0; i < s->req.u.rw.nr_segments; i++) {
>> + for (i = 0; i < nseg; i++) {
>> list_add(&s->grants_used[i]->node, &info->persistent_gnts);
>> info->persistent_gnts_c++;
>> }
>> + if (s->req.operation == BLKIF_OP_INDIRECT) {
>> + for (i = 0; i < INDIRECT_GREFS(nseg); i++) {
>> + list_add(&s->indirect_grants[i]->node,
>> + &info->persistent_gnts);
>
> One line pls.
>
>> + info->persistent_gnts_c++;
>> + }
>> + }
>> }
>>
>> static irqreturn_t blkif_interrupt(int irq, void *dev_id)
>> @@ -1034,14 +1168,6 @@ static int setup_blkring(struct xenbus_device *dev,
>> SHARED_RING_INIT(sring);
>> FRONT_RING_INIT(&info->ring, sring, PAGE_SIZE);
>>
>> - sg_init_table(info->sg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
>> -
>> - /* Allocate memory for grants */
>> - err = fill_grant_buffer(info, BLK_RING_SIZE *
>> - BLKIF_MAX_SEGMENTS_PER_REQUEST);
>> - if (err)
>> - goto fail;
>> -
>> err = xenbus_grant_ring(dev, virt_to_mfn(info->ring.sring));
>> if (err < 0) {
>> free_page((unsigned long)sring);
>> @@ -1223,13 +1349,84 @@ static int blkfront_probe(struct xenbus_device *dev,
>> return 0;
>> }
>>
>> +/*
>> + * This is a clone of md_trim_bio, used to split a bio into smaller ones
>> + */
>> +static void trim_bio(struct bio *bio, int offset, int size)
>> +{
>> + /* 'bio' is a cloned bio which we need to trim to match
>> + * the given offset and size.
>> + * This requires adjusting bi_sector, bi_size, and bi_io_vec
>> + */
>> + int i;
>> + struct bio_vec *bvec;
>> + int sofar = 0;
>> +
>> + size <<= 9;
>> + if (offset == 0 && size == bio->bi_size)
>> + return;
>> +
>> + bio->bi_sector += offset;
>> + bio->bi_size = size;
>> + offset <<= 9;
>> + clear_bit(BIO_SEG_VALID, &bio->bi_flags);
>> +
>> + while (bio->bi_idx < bio->bi_vcnt &&
>> + bio->bi_io_vec[bio->bi_idx].bv_len <= offset) {
>> + /* remove this whole bio_vec */
>> + offset -= bio->bi_io_vec[bio->bi_idx].bv_len;
>> + bio->bi_idx++;
>> + }
>> + if (bio->bi_idx < bio->bi_vcnt) {
>> + bio->bi_io_vec[bio->bi_idx].bv_offset += offset;
>> + bio->bi_io_vec[bio->bi_idx].bv_len -= offset;
>> + }
>> + /* avoid any complications with bi_idx being non-zero*/
>> + if (bio->bi_idx) {
>> + memmove(bio->bi_io_vec, bio->bi_io_vec+bio->bi_idx,
>> + (bio->bi_vcnt - bio->bi_idx) * sizeof(struct bio_vec));
>> + bio->bi_vcnt -= bio->bi_idx;
>> + bio->bi_idx = 0;
>> + }
>> + /* Make sure vcnt and last bv are not too big */
>> + bio_for_each_segment(bvec, bio, i) {
>> + if (sofar + bvec->bv_len > size)
>> + bvec->bv_len = size - sofar;
>> + if (bvec->bv_len == 0) {
>> + bio->bi_vcnt = i;
>> + break;
>> + }
>> + sofar += bvec->bv_len;
>> + }
>> +}
>> +
>> +static void split_bio_end(struct bio *bio, int error)
>> +{
>> + struct split_bio *split_bio = bio->bi_private;
>> +
>> + if (error)
>> + split_bio->err = error;
>> +
>> + if (atomic_dec_and_test(&split_bio->pending)) {
>> + split_bio->bio->bi_phys_segments = 0;
>> + bio_endio(split_bio->bio, split_bio->err);
>> + kfree(split_bio);
>> + }
>> + bio_put(bio);
>> +}
>>
>> static int blkif_recover(struct blkfront_info *info)
>> {
>> int i;
>> - struct blkif_request *req;
>> + struct request *req, *n;
>> struct blk_shadow *copy;
>> - int j;
>> + int rc;
>> + struct bio *bio, *cloned_bio;
>> + struct bio_list bio_list, merge_bio;
>> + unsigned int segs;
>> + int pending, offset, size;
>> + struct split_bio *split_bio;
>> + struct list_head requests;
>>
>> /* Stage 1: Make a safe copy of the shadow state. */
>> copy = kmemdup(info->shadow, sizeof(info->shadow),
>> @@ -1244,36 +1441,64 @@ static int blkif_recover(struct blkfront_info *info)
>> info->shadow_free = info->ring.req_prod_pvt;
>> info->shadow[BLK_RING_SIZE-1].req.u.rw.id = 0x0fffffff;
>>
>> - /* Stage 3: Find pending requests and requeue them. */
>> + rc = blkfront_setup_indirect(info);
>> + if (rc) {
>> + kfree(copy);
>> + return rc;
>> + }
>> +
>> + segs = info->max_indirect_segments ? : BLKIF_MAX_SEGMENTS_PER_REQUEST;
>> + blk_queue_max_segments(info->rq, segs);
>> + bio_list_init(&bio_list);
>> + INIT_LIST_HEAD(&requests);
>> for (i = 0; i < BLK_RING_SIZE; i++) {
>> /* Not in use? */
>> if (!copy[i].request)
>> continue;
>>
>> - /* Grab a request slot and copy shadow state into it. */
>> - req = RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt);
>> - *req = copy[i].req;
>> -
>> - /* We get a new request id, and must reset the shadow state. */
>> - req->u.rw.id = get_id_from_freelist(info);
>> - memcpy(&info->shadow[req->u.rw.id], ©[i], sizeof(copy[i]));
>> -
>> - if (req->operation != BLKIF_OP_DISCARD) {
>> - /* Rewrite any grant references invalidated by susp/resume. */
>> - for (j = 0; j < req->u.rw.nr_segments; j++)
>> - gnttab_grant_foreign_access_ref(
>> - req->u.rw.seg[j].gref,
>> - info->xbdev->otherend_id,
>> - pfn_to_mfn(copy[i].grants_used[j]->pfn),
>> - 0);
>> + /*
>> + * Get the bios in the request so we can re-queue them.
>> + */
>> + if (copy[i].request->cmd_flags &
>> + (REQ_FLUSH | REQ_FUA | REQ_DISCARD | REQ_SECURE)) {
>> + /*
>> + * Flush operations don't contain bios, so
>> + * we need to requeue the whole request
>> + */
>> + list_add(©[i].request->queuelist, &requests);
>> + continue;
>> }
>> - info->shadow[req->u.rw.id].req = *req;
>> -
>> - info->ring.req_prod_pvt++;
>> + merge_bio.head = copy[i].request->bio;
>> + merge_bio.tail = copy[i].request->biotail;
>> + bio_list_merge(&bio_list, &merge_bio);
>> + copy[i].request->bio = NULL;
>> + blk_put_request(copy[i].request);
>> }
>>
>> kfree(copy);
>>
>> + /*
>> + * Empty the queue, this is important because we might have
>> + * requests in the queue with more segments than what we
>> + * can handle now.
>> + */
>> + spin_lock_irq(&info->io_lock);
>> + while ((req = blk_fetch_request(info->rq)) != NULL) {
>> + if (req->cmd_flags &
>> + (REQ_FLUSH | REQ_FUA | REQ_DISCARD | REQ_SECURE)) {
>> + list_add(&req->queuelist, &requests);
>> + continue;
>> + }
>> + merge_bio.head = req->bio;
>> + merge_bio.tail = req->biotail;
>> + bio_list_merge(&bio_list, &merge_bio);
>> + req->bio = NULL;
>> + if (req->cmd_flags & (REQ_FLUSH | REQ_FUA))
>> + pr_alert("diskcache flush request found!\n");
>> + __blk_put_request(info->rq, req);
>> + }
>> + spin_unlock_irq(&info->io_lock);
>> +
>> xenbus_switch_state(info->xbdev, XenbusStateConnected);
>>
>> spin_lock_irq(&info->io_lock);
>> @@ -1281,14 +1506,50 @@ static int blkif_recover(struct blkfront_info *info)
>> /* Now safe for us to use the shared ring */
>> info->connected = BLKIF_STATE_CONNECTED;
>>
>> - /* Send off requeued requests */
>> - flush_requests(info);
>> -
>> /* Kick any other new requests queued since we resumed */
>> kick_pending_request_queues(info);
>>
>> + list_for_each_entry_safe(req, n, &requests, queuelist) {
>> + /* Requeue pending requests (flush or discard) */
>> + list_del_init(&req->queuelist);
>> + BUG_ON(req->nr_phys_segments > segs);
>> + blk_requeue_request(info->rq, req);
>> + }
>> spin_unlock_irq(&info->io_lock);
>>
>> + while ((bio = bio_list_pop(&bio_list)) != NULL) {
>> + /* Traverse the list of pending bios and re-queue them */
>> + if (bio_segments(bio) > segs) {
>> + /*
>> + * This bio has more segments than what we can
>> + * handle, we have to split it.
>> + */
>> + pending = (bio_segments(bio) + segs - 1) / segs;
>> + split_bio = kzalloc(sizeof(*split_bio), GFP_NOIO);
>> + BUG_ON(split_bio == NULL);
>> + atomic_set(&split_bio->pending, pending);
>> + split_bio->bio = bio;
>> + for (i = 0; i < pending; i++) {
>> + offset = (i * segs * PAGE_SIZE) >> 9;
>> + size = MIN((segs * PAGE_SIZE) >> 9,
>> + (bio->bi_size >> 9) - offset);
>> + cloned_bio = bio_clone(bio, GFP_NOIO);
>> + BUG_ON(cloned_bio == NULL);
>> + trim_bio(cloned_bio, offset, size);
>> + cloned_bio->bi_private = split_bio;
>> + cloned_bio->bi_end_io = split_bio_end;
>> + submit_bio(cloned_bio->bi_rw, cloned_bio);
>> + }
>> + /*
>> + * Now we have to wait for all those smaller bios to
>> + * end, so we can also end the "parent" bio.
>> + */
>> + continue;
>> + }
>> + /* We don't need to split this bio */
>> + submit_bio(bio->bi_rw, bio);
>> + }
>> +
>> return 0;
>> }
>>
>> @@ -1308,8 +1569,12 @@ static int blkfront_resume(struct xenbus_device *dev)
>> blkif_free(info, info->connected == BLKIF_STATE_CONNECTED);
>>
>> err = talk_to_blkback(dev, info);
>> - if (info->connected == BLKIF_STATE_SUSPENDED && !err)
>> - err = blkif_recover(info);
>> +
>> + /*
>> + * We have to wait for the backend to switch to
>> + * connected state, since we want to read which
>> + * features it supports.
>> + */
>>
>> return err;
>> }
>> @@ -1387,6 +1652,62 @@ static void blkfront_setup_discard(struct blkfront_info *info)
>> kfree(type);
>> }
>>
>> +static int blkfront_setup_indirect(struct blkfront_info *info)
>> +{
>> + unsigned int indirect_segments, segs;
>> + int err, i;
>> +
>> + err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
>> + "max-indirect-segments", "%u", &indirect_segments,
>
> That I believe has to be 'feature-max-indirect-segments'
Yes, I've changed it in blkfront and blkback.
>
>> + NULL);
>> + if (err) {
>> + info->max_indirect_segments = 0;
>> + segs = BLKIF_MAX_SEGMENTS_PER_REQUEST;
>> + } else {
>> + info->max_indirect_segments = MIN(indirect_segments,
>> + xen_blkif_max_segments);
>> + segs = info->max_indirect_segments;
>> + }
>> + info->sg = kzalloc(sizeof(info->sg[0]) * segs, GFP_KERNEL);
>> + if (info->sg == NULL)
>> + goto out_of_memory;
>> + sg_init_table(info->sg, segs);
>> +
>> + err = fill_grant_buffer(info,
>> + (segs + INDIRECT_GREFS(segs)) * BLK_RING_SIZE);
>> + if (err)
>> + goto out_of_memory;
>> +
>> + for (i = 0; i < BLK_RING_SIZE; i++) {
>> + info->shadow[i].grants_used = kzalloc(
>> + sizeof(info->shadow[i].grants_used[0]) * segs,
>> + GFP_NOIO);
>> + if (info->max_indirect_segments)
>> + info->shadow[i].indirect_grants = kzalloc(
>> + sizeof(info->shadow[i].indirect_grants[0]) *
>> + INDIRECT_GREFS(segs),
>> + GFP_NOIO);
>> + if ((info->shadow[i].grants_used == NULL) ||
>> + (info->max_indirect_segments &&
>> + (info->shadow[i].indirect_grants == NULL)))
>> + goto out_of_memory;
>> + }
>> +
>> +
>> + return 0;
>> +
>> +out_of_memory:
>> + kfree(info->sg);
>> + info->sg = NULL;
>> + for (i = 0; i < BLK_RING_SIZE; i++) {
>> + kfree(info->shadow[i].grants_used);
>> + info->shadow[i].grants_used = NULL;
>> + kfree(info->shadow[i].indirect_grants);
>> + info->shadow[i].indirect_grants = NULL;
>> + }
>> + return -ENOMEM;
>> +}
>> +
>> /*
>> * Invoked when the backend is finally 'ready' (and has told produced
>> * the details about the physical device - #sectors, size, etc).
>> @@ -1414,8 +1735,9 @@ static void blkfront_connect(struct blkfront_info *info)
>> set_capacity(info->gd, sectors);
>> revalidate_disk(info->gd);
>>
>> - /* fall through */
>> + return;
>
> How come?
We cannot fall thought anymore, because now we call blkif_recover in
order to recover after performing the suspension, in the past this was
just a return so we could fall thought.
We need to perform the recover at this point because we need to know if
the backend supports indirect descriptors, and how many. In the past we
used to perform the recover before the backend announced it's features,
but now we need to know if the backend supports indirect segments or not.
>
>> case BLKIF_STATE_SUSPENDED:
>> + blkif_recover(info);
>> return;
>>
>> default:
>> @@ -1436,6 +1758,7 @@ static void blkfront_connect(struct blkfront_info *info)
>> info->xbdev->otherend);
>> return;
>> }
>> + info->sector_size = sector_size;
>>
>> info->feature_flush = 0;
>> info->flush_op = 0;
>> @@ -1483,6 +1806,13 @@ static void blkfront_connect(struct blkfront_info *info)
>> else
>> info->feature_persistent = persistent;
>>
>> + err = blkfront_setup_indirect(info);
>> + if (err) {
>> + xenbus_dev_fatal(info->xbdev, err, "setup_indirect at %s",
>> + info->xbdev->otherend);
>> + return;
>> + }
>> +
>> err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size);
>> if (err) {
>> xenbus_dev_fatal(info->xbdev, err, "xlvbd_add at %s",
>> diff --git a/include/xen/interface/io/blkif.h b/include/xen/interface/io/blkif.h
>> index ffd4652..893bee2 100644
>> --- a/include/xen/interface/io/blkif.h
>> +++ b/include/xen/interface/io/blkif.h
>> @@ -102,6 +102,8 @@ typedef uint64_t blkif_sector_t;
>> */
>> #define BLKIF_OP_DISCARD 5
>>
>> +#define BLKIF_OP_INDIRECT 6
>> +
>
> Ahem! There needs to be more about this. For example which 'feature-X' sets it,
> what kind of operations are permitted, etc.
>
>> /*
>> * Maximum scatter/gather segments per request.
>> * This is carefully chosen so that sizeof(struct blkif_ring) <= PAGE_SIZE.
>> @@ -109,6 +111,16 @@ typedef uint64_t blkif_sector_t;
>> */
>> #define BLKIF_MAX_SEGMENTS_PER_REQUEST 11
>>
>> +#define BLKIF_MAX_INDIRECT_GREFS_PER_REQUEST 8
>> +
>> +struct blkif_request_segment_aligned {
>> + grant_ref_t gref; /* reference to I/O buffer frame */
>> + /* @first_sect: first sector in frame to transfer (inclusive). */
>> + /* @last_sect: last sector in frame to transfer (inclusive). */
>> + uint8_t first_sect, last_sect;
>> + uint16_t _pad; /* padding to make it 8 bytes, so it's cache-aligned */
>> +} __attribute__((__packed__));
>> +
>> struct blkif_request_rw {
>> uint8_t nr_segments; /* number of segments */
>> blkif_vdev_t handle; /* only for read/write requests */
>> @@ -147,12 +159,26 @@ struct blkif_request_other {
>> uint64_t id; /* private guest value, echoed in resp */
>> } __attribute__((__packed__));
>>
>> +struct blkif_request_indirect {
>> + uint8_t indirect_op;
>> + uint16_t nr_segments;
>> +#ifdef CONFIG_X86_64
>> + uint32_t _pad1; /* offsetof(blkif_...,u.indirect.id) == 8 */
>> +#endif
>> + uint64_t id;
>> + blkif_sector_t sector_number;
>> + blkif_vdev_t handle;
>> + uint16_t _pad2;
>> + grant_ref_t indirect_grefs[BLKIF_MAX_INDIRECT_GREFS_PER_REQUEST];
>> +} __attribute__((__packed__));
>> +
>> struct blkif_request {
>> uint8_t operation; /* BLKIF_OP_??? */
>> union {
>> struct blkif_request_rw rw;
>> struct blkif_request_discard discard;
>> struct blkif_request_other other;
>> + struct blkif_request_indirect indirect;
>> } u;
>> } __attribute__((__packed__));
>>
>> --
>> 1.7.7.5 (Apple Git-26)
>>
--
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