Date:	Fri, 15 May 2015 13:13:21 +0200
From:	Roger Pau Monné <roger.pau@...rix.com>
To:	Bob Liu <bob.liu@...cle.com>, <xen-devel@...ts.xen.org>
CC:	<david.vrabel@...rix.com>, <justing@...ctralogic.com>,
	<konrad.wilk@...cle.com>, <paul.durrant@...rix.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] xen/block: add multi-page ring support

El 12/05/15 a les 13.01, Bob Liu ha escrit:
> Extend xen/block to support multi-page ring, so that more requests can be issued
> by using more than one pages as the request ring between blkfront and backend.
> As a result, the performance can get improved significantly.
                              ^ s/can get improved/improves/

> 
> We got some impressive improvements on our highend iscsi storage cluster backend.
> If using 64 pages as the ring, the IOPS increased about 15 times for the
> throughput testing and above doubled for the latency testing.
> 
> The reason was the limit on outstanding requests is 32 if use only one-page
> ring, but in our case the iscsi lun was spread across about 100 physical drives,
> 32 was really not enough to keep them busy.
> 
> Changes in v2:
>  - Rebased to 4.0-rc6
>  - Added description on how this protocol works into io/blkif.h

I don't see any changes to io/blkif.h in this patch, is something missing?

Also you use XENBUS_MAX_RING_PAGES which AFAICT it's not defined anywhere.

> 
> Changes in v3:
>  - Follow the protocol defined in io/blkif.h on XEN tree
> 
> Signed-off-by: Bob Liu <bob.liu@...cle.com>
> ---
>  drivers/block/xen-blkback/blkback.c |  14 ++++-
>  drivers/block/xen-blkback/common.h  |   4 +-
>  drivers/block/xen-blkback/xenbus.c  |  83 ++++++++++++++++++++++-------
>  drivers/block/xen-blkfront.c        | 102 +++++++++++++++++++++++++++---------
>  4 files changed, 156 insertions(+), 47 deletions(-)
> 
> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
> index 713fc9f..f191083 100644
> --- a/drivers/block/xen-blkback/blkback.c
> +++ b/drivers/block/xen-blkback/blkback.c
> @@ -84,6 +84,12 @@ MODULE_PARM_DESC(max_persistent_grants,
>                   "Maximum number of grants to map persistently");
>  
>  /*
> + * Maximum number of pages to be used as the ring between front and backend
> + */
> +unsigned int xen_blkif_max_ring_pages = XENBUS_MAX_RING_PAGES;
> +module_param_named(max_ring_pages, xen_blkif_max_ring_pages, int, S_IRUGO);
> +MODULE_PARM_DESC(max_ring_pages, "Maximum amount of pages to be used as the ring");
> +/*
>   * The LRU mechanism to clean the lists of persistent grants needs to
>   * be executed periodically. The time interval between consecutive executions
>   * of the purge mechanism is set in ms.
> @@ -630,7 +636,7 @@ purge_gnt_list:
>  		}
>  
>  		/* Shrink if we have more than xen_blkif_max_buffer_pages */
> -		shrink_free_pagepool(blkif, xen_blkif_max_buffer_pages);
> +		shrink_free_pagepool(blkif, xen_blkif_max_buffer_pages * blkif->nr_ring_pages);

You are greatly increasing the buffer of free (ballooned) pages.
Possibly making it 32 times bigger than it used to be, is this really
needed?

>  
>  		if (log_stats && time_after(jiffies, blkif->st_print))
>  			print_stats(blkif);
> @@ -1435,6 +1441,12 @@ static int __init xen_blkif_init(void)
>  {
>  	int rc = 0;
>  
> +	if (xen_blkif_max_ring_pages > XENBUS_MAX_RING_PAGES) {
> +		pr_info("Invalid max_ring_pages (%d), will use default max: %d.\n",
> +			xen_blkif_max_ring_pages, XENBUS_MAX_RING_PAGES);
> +		xen_blkif_max_ring_pages = XENBUS_MAX_RING_PAGES;
> +	}
> +
>  	if (!xen_domain())
>  		return -ENODEV;
>  
> diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
> index f620b5d..84a964c 100644
> --- a/drivers/block/xen-blkback/common.h
> +++ b/drivers/block/xen-blkback/common.h
> @@ -44,6 +44,7 @@
>  #include <xen/interface/io/blkif.h>
>  #include <xen/interface/io/protocols.h>
>  
> +extern unsigned int xen_blkif_max_ring_pages;
>  /*
>   * This is the maximum number of segments that would be allowed in indirect
>   * requests. This value will also be passed to the frontend.
> @@ -248,7 +249,7 @@ struct backend_info;
>  #define PERSISTENT_GNT_WAS_ACTIVE	1
>  
>  /* Number of requests that we can fit in a ring */
> -#define XEN_BLKIF_REQS			32
> +#define XEN_BLKIF_REQS			(32 * XENBUS_MAX_RING_PAGES)

This should be made a member of xen_blkif and set dynamically, or else
we are just wasting memory if the frontend doesn't support multipage
rings. We seem to be doing this for a bunch of features, but allocating
32 times the needed amount of requests (if the frontend doesn't support
multipage rings) seems too much IMHO.

>  
>  struct persistent_gnt {
>  	struct page *page;
> @@ -320,6 +321,7 @@ struct xen_blkif {
>  	struct work_struct	free_work;
>  	/* Thread shutdown wait queue. */
>  	wait_queue_head_t	shutdown_wq;
> +	int nr_ring_pages;
>  };
>  
>  struct seg_buf {
> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> index 6ab69ad..909babd 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -198,8 +198,8 @@ fail:
>  	return ERR_PTR(-ENOMEM);
>  }
>  
> -static int xen_blkif_map(struct xen_blkif *blkif, grant_ref_t gref,
> -			 unsigned int evtchn)
> +static int xen_blkif_map(struct xen_blkif *blkif, grant_ref_t *gref,
> +			 unsigned int nr_grefs, unsigned int evtchn)
>  {
>  	int err;
>  
> @@ -207,7 +207,7 @@ static int xen_blkif_map(struct xen_blkif *blkif, grant_ref_t gref,
>  	if (blkif->irq)
>  		return 0;
>  
> -	err = xenbus_map_ring_valloc(blkif->be->dev, &gref, 1,
> +	err = xenbus_map_ring_valloc(blkif->be->dev, gref, nr_grefs,
>  				     &blkif->blk_ring);
>  	if (err < 0)
>  		return err;
> @@ -217,21 +217,21 @@ static int xen_blkif_map(struct xen_blkif *blkif, grant_ref_t gref,
>  	{
>  		struct blkif_sring *sring;
>  		sring = (struct blkif_sring *)blkif->blk_ring;
> -		BACK_RING_INIT(&blkif->blk_rings.native, sring, PAGE_SIZE);
> +		BACK_RING_INIT(&blkif->blk_rings.native, sring, PAGE_SIZE * nr_grefs);
>  		break;
>  	}
>  	case BLKIF_PROTOCOL_X86_32:
>  	{
>  		struct blkif_x86_32_sring *sring_x86_32;
>  		sring_x86_32 = (struct blkif_x86_32_sring *)blkif->blk_ring;
> -		BACK_RING_INIT(&blkif->blk_rings.x86_32, sring_x86_32, PAGE_SIZE);
> +		BACK_RING_INIT(&blkif->blk_rings.x86_32, sring_x86_32, PAGE_SIZE * nr_grefs);
>  		break;
>  	}
>  	case BLKIF_PROTOCOL_X86_64:
>  	{
>  		struct blkif_x86_64_sring *sring_x86_64;
>  		sring_x86_64 = (struct blkif_x86_64_sring *)blkif->blk_ring;
> -		BACK_RING_INIT(&blkif->blk_rings.x86_64, sring_x86_64, PAGE_SIZE);
> +		BACK_RING_INIT(&blkif->blk_rings.x86_64, sring_x86_64, PAGE_SIZE * nr_grefs);
>  		break;
>  	}
>  	default:
> @@ -597,6 +597,11 @@ static int xen_blkbk_probe(struct xenbus_device *dev,
>  	if (err)
>  		goto fail;
>  
> +	err = xenbus_printf(XBT_NIL, dev->nodename, "max-ring-pages", "%u",
> +			    xen_blkif_max_ring_pages);
> +	if (err)
> +		pr_warn("%s write out 'max-ring-pages' failed\n", __func__);
> +
>  	err = xenbus_switch_state(dev, XenbusStateInitWait);
>  	if (err)
>  		goto fail;
> @@ -860,22 +865,62 @@ again:
>  static int connect_ring(struct backend_info *be)
>  {
>  	struct xenbus_device *dev = be->dev;
> -	unsigned long ring_ref;
> -	unsigned int evtchn;
> +	unsigned int ring_ref[XENBUS_MAX_RING_PAGES];
> +	unsigned int evtchn, nr_grefs;
>  	unsigned int pers_grants;
>  	char protocol[64] = "";
>  	int err;
>  
>  	pr_debug("%s %s\n", __func__, dev->otherend);
>  
> -	err = xenbus_gather(XBT_NIL, dev->otherend, "ring-ref", "%lu",
> -			    &ring_ref, "event-channel", "%u", &evtchn, NULL);
> -	if (err) {
> -		xenbus_dev_fatal(dev, err,
> -				 "reading %s/ring-ref and event-channel",
> +	err = xenbus_scanf(XBT_NIL, dev->otherend, "event-channel", "%u",
> +			  &evtchn);
> +	if (err != 1) {
> +		err = -EINVAL;
> +		xenbus_dev_fatal(dev, err, "reading %s/event-channel",
>  				 dev->otherend);
>  		return err;
>  	}
> +	pr_info("event-channel %u\n", evtchn);
> +
> +	err = xenbus_scanf(XBT_NIL, dev->otherend, "num-ring-pages", "%u",
> +			  &nr_grefs);
> +	if (err != 1) {
> +		err = xenbus_scanf(XBT_NIL, dev->otherend, "ring-ref",
> +				  "%u", &ring_ref[0]);
> +		if (err != 1) {
> +			err = -EINVAL;
> +			xenbus_dev_fatal(dev, err, "reading %s/ring-ref",
> +					 dev->otherend);
> +			return err;
> +		}
> +		nr_grefs = 1;
> +		pr_info("%s:using single page: ring-ref %d\n", dev->otherend,
> +			ring_ref[0]);
> +	} else {
> +		unsigned int i;
> +
> +		if (nr_grefs > xen_blkif_max_ring_pages) {
> +			err = -EINVAL;
> +			xenbus_dev_fatal(dev, err, "%s/request %d ring pages exceed max:%d",
> +					 dev->otherend, nr_grefs, xen_blkif_max_ring_pages);
> +			return err;
> +		}
> +		for (i = 0; i < nr_grefs; i++) {
> +			char ring_ref_name[BLKBACK_NAME_LEN];

I would add a new macro rather than reusing one which might change
(BLKBACK_RINGREF_LEN?).

> +
> +			snprintf(ring_ref_name, sizeof(ring_ref_name), "ring-ref%u", i);
> +			err = xenbus_scanf(XBT_NIL, dev->otherend,
> +					   ring_ref_name, "%u", &ring_ref[i]);
> +			if (err != 1) {
> +				err = -EINVAL;
> +				xenbus_dev_fatal(dev, err, "reading %s/%s",
> +						 dev->otherend, ring_ref_name);
> +				return err;
> +			}
> +			pr_info("ring-ref%u: %u\n", i, ring_ref[i]);
> +		}
> +	}
>  
>  	be->blkif->blk_protocol = BLKIF_PROTOCOL_DEFAULT;
>  	err = xenbus_gather(XBT_NIL, dev->otherend, "protocol",
> @@ -900,16 +945,16 @@ static int connect_ring(struct backend_info *be)
>  
>  	be->blkif->vbd.feature_gnt_persistent = pers_grants;
>  	be->blkif->vbd.overflow_max_grants = 0;
> +	be->blkif->nr_ring_pages = nr_grefs;
>  
> -	pr_info("ring-ref %ld, event-channel %d, protocol %d (%s) %s\n",
> -		ring_ref, evtchn, be->blkif->blk_protocol, protocol,
> -		pers_grants ? "persistent grants" : "");
> +	pr_info("ring-pages:%d, event-channel %d, protocol %d (%s) %s\n",
> +			nr_grefs, evtchn, be->blkif->blk_protocol, protocol,
> +			pers_grants ? "persistent grants" : "");
>  
>  	/* Map the shared frame, irq etc. */
> -	err = xen_blkif_map(be->blkif, ring_ref, evtchn);
> +	err = xen_blkif_map(be->blkif, ring_ref, nr_grefs, evtchn);
>  	if (err) {
> -		xenbus_dev_fatal(dev, err, "mapping ring-ref %lu port %u",
> -				 ring_ref, evtchn);
> +		xenbus_dev_fatal(dev, err, "mapping ring-ref port %u", evtchn);
>  		return err;
>  	}
>  
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 88e23fd..c4b427f 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -98,7 +98,17 @@ static unsigned int xen_blkif_max_segments = 32;
>  module_param_named(max, xen_blkif_max_segments, int, S_IRUGO);
>  MODULE_PARM_DESC(max, "Maximum amount of segments in indirect requests (default is 32)");
>  
> -#define BLK_RING_SIZE __CONST_RING_SIZE(blkif, PAGE_SIZE)
> +static unsigned int xen_blkif_max_ring_pages = 1;
> +module_param_named(max_ring_pages, xen_blkif_max_ring_pages, int, S_IRUGO);
> +MODULE_PARM_DESC(max_ring_pages, "Maximum amount of pages to be used as the ring");
> +
> +#define BLK_RING_SIZE __CONST_RING_SIZE(blkif, PAGE_SIZE * info->nr_ring_pages)

I would prefer if this macro took a explicit info parameter instead on
realying that it is always info.

> +#define BLK_MAX_RING_SIZE __CONST_RING_SIZE(blkif, PAGE_SIZE * XENBUS_MAX_RING_PAGES)
> +/*
> + * ring-ref%i i=(-1UL) would take 11 characters + 'ring-ref' is 8, so 19 characters
> + * are enough. Define to 20 to keep consist with backend.
> + */
> +#define RINGREF_NAME_LEN (20)
>  
>  /*
>   * We have one of these per vbd, whether ide, scsi or 'other'.  They
> @@ -114,13 +124,14 @@ struct blkfront_info
>  	int vdevice;
>  	blkif_vdev_t handle;
>  	enum blkif_state connected;
> -	int ring_ref;
> +	int ring_ref[XENBUS_MAX_RING_PAGES];
> +	unsigned int nr_ring_pages;
>  	struct blkif_front_ring ring;
>  	unsigned int evtchn, irq;
>  	struct request_queue *rq;
>  	struct work_struct work;
>  	struct gnttab_free_callback callback;
> -	struct blk_shadow shadow[BLK_RING_SIZE];
> +	struct blk_shadow shadow[BLK_MAX_RING_SIZE];
>  	struct list_head grants;
>  	struct list_head indirect_pages;
>  	unsigned int persistent_gnts_c;
> @@ -139,8 +150,6 @@ static unsigned int nr_minors;
>  static unsigned long *minors;
>  static DEFINE_SPINLOCK(minor_lock);
>  
> -#define MAXIMUM_OUTSTANDING_BLOCK_REQS \
> -	(BLKIF_MAX_SEGMENTS_PER_REQUEST * BLK_RING_SIZE)
>  #define GRANT_INVALID_REF	0
>  
>  #define PARTS_PER_DISK		16
> @@ -1033,12 +1042,15 @@ free_shadow:
>  	flush_work(&info->work);
>  
>  	/* Free resources associated with old device channel. */
> -	if (info->ring_ref != GRANT_INVALID_REF) {
> -		gnttab_end_foreign_access(info->ring_ref, 0,
> -					  (unsigned long)info->ring.sring);
> -		info->ring_ref = GRANT_INVALID_REF;
> -		info->ring.sring = NULL;
> +	for (i = 0; i < info->nr_ring_pages; i++) {
> +		if (info->ring_ref[i] != GRANT_INVALID_REF) {
> +			gnttab_end_foreign_access(info->ring_ref[i], 0, 0);
> +			info->ring_ref[i] = GRANT_INVALID_REF;
> +		}
>  	}
> +	free_pages((unsigned long)info->ring.sring, get_order(info->nr_ring_pages * PAGE_SIZE));
> +	info->ring.sring = NULL;
> +
>  	if (info->irq)
>  		unbind_from_irqhandler(info->irq, info);
>  	info->evtchn = info->irq = 0;
> @@ -1245,26 +1257,30 @@ static int setup_blkring(struct xenbus_device *dev,
>  			 struct blkfront_info *info)
>  {
>  	struct blkif_sring *sring;
> -	grant_ref_t gref;
> -	int err;
> +	int err, i;
> +	unsigned long ring_size = info->nr_ring_pages * PAGE_SIZE;
> +	grant_ref_t gref[XENBUS_MAX_RING_PAGES];
>  
> -	info->ring_ref = GRANT_INVALID_REF;
> +	for (i = 0; i < info->nr_ring_pages; i++)
> +		info->ring_ref[i] = GRANT_INVALID_REF;
>  
> -	sring = (struct blkif_sring *)__get_free_page(GFP_NOIO | __GFP_HIGH);
> +	sring = (struct blkif_sring *)__get_free_pages(GFP_NOIO | __GFP_HIGH,
> +						       get_order(ring_size));
>  	if (!sring) {
>  		xenbus_dev_fatal(dev, -ENOMEM, "allocating shared ring");
>  		return -ENOMEM;
>  	}
>  	SHARED_RING_INIT(sring);
> -	FRONT_RING_INIT(&info->ring, sring, PAGE_SIZE);
> +	FRONT_RING_INIT(&info->ring, sring, ring_size);
>  
> -	err = xenbus_grant_ring(dev, info->ring.sring, 1, &gref);
> +	err = xenbus_grant_ring(dev, info->ring.sring, info->nr_ring_pages, gref);
>  	if (err < 0) {
>  		free_page((unsigned long)sring);
>  		info->ring.sring = NULL;
>  		goto fail;
>  	}
> -	info->ring_ref = gref;
> +	for (i = 0; i < info->nr_ring_pages; i++)
> +		info->ring_ref[i] = gref[i];
>  
>  	err = xenbus_alloc_evtchn(dev, &info->evtchn);
>  	if (err)
> @@ -1292,7 +1308,15 @@ static int talk_to_blkback(struct xenbus_device *dev,
>  {
>  	const char *message = NULL;
>  	struct xenbus_transaction xbt;
> -	int err;
> +	int err, i;
> +	unsigned int max_pages = 0;
> +
> +	err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
> +			   "max-ring-pages", "%u", &max_pages);
> +	if (err != 1)
> +		info->nr_ring_pages = 1;
> +	else
> +		info->nr_ring_pages = min(xen_blkif_max_ring_pages, max_pages);
>  
>  	/* Create shared ring, alloc event channel. */
>  	err = setup_blkring(dev, info);
> @@ -1306,11 +1330,31 @@ again:
>  		goto destroy_blkring;
>  	}
>  
> -	err = xenbus_printf(xbt, dev->nodename,
> -			    "ring-ref", "%u", info->ring_ref);
> -	if (err) {
> -		message = "writing ring-ref";
> -		goto abort_transaction;
> +	if (info->nr_ring_pages == 1) {
> +		err = xenbus_printf(xbt, dev->nodename,
> +				    "ring-ref", "%u", info->ring_ref[0]);
> +		if (err) {
> +			message = "writing ring-ref";
> +			goto abort_transaction;
> +		}
> +	} else {
> +		err = xenbus_printf(xbt, dev->nodename,
> +				    "num-ring-pages", "%u", info->nr_ring_pages);
> +		if (err) {
> +			message = "writing num-ring-pages";
> +			goto abort_transaction;
> +		}
> +
> +		for (i = 0; i < info->nr_ring_pages; i++) {
> +			char ring_ref_name[RINGREF_NAME_LEN];
> +			snprintf(ring_ref_name, sizeof(ring_ref_name), "ring-ref%u", i);
> +			err = xenbus_printf(xbt, dev->nodename,
> +					ring_ref_name, "%u", info->ring_ref[i]);
> +			if (err) {
> +				message = "writing ring-ref";
> +				goto abort_transaction;
> +			}
> +		}
>  	}
>  	err = xenbus_printf(xbt, dev->nodename,
>  			    "event-channel", "%u", info->evtchn);
> @@ -1338,6 +1382,7 @@ again:
>  		goto destroy_blkring;
>  	}

Why is this moved to here...

> +	info->shadow[BLK_RING_SIZE-1].req.u.rw.id = 0x0fffffff;
>  	xenbus_switch_state(dev, XenbusStateInitialised);
>  
>  	return 0;
> @@ -1422,9 +1467,8 @@ static int blkfront_probe(struct xenbus_device *dev,
>  	info->connected = BLKIF_STATE_DISCONNECTED;
>  	INIT_WORK(&info->work, blkif_restart_queue);
>  
> -	for (i = 0; i < BLK_RING_SIZE; i++)
> +	for (i = 0; i < BLK_MAX_RING_SIZE; i++)
>  		info->shadow[i].req.u.rw.id = i+1;
> -	info->shadow[BLK_RING_SIZE-1].req.u.rw.id = 0x0fffffff;

from here. Isn't the previous location suitable anymore?

Also, if BLK_RING_SIZE < BLK_MAX_RING_SIZE you are overwriting the
previously written value in the above loop.

>  
>  	/* Front end dir is a number, which is used as the id. */
>  	info->handle = simple_strtoul(strrchr(dev->nodename, '/')+1, NULL, 0);
> @@ -1469,7 +1513,7 @@ static int blkif_recover(struct blkfront_info *info)
>  
>  	/* Stage 2: Set up free list. */
>  	memset(&info->shadow, 0, sizeof(info->shadow));
> -	for (i = 0; i < BLK_RING_SIZE; i++)
> +	for (i = 0; i < BLK_MAX_RING_SIZE; i++)
>  		info->shadow[i].req.u.rw.id = i+1;
>  	info->shadow_free = info->ring.req_prod_pvt;
>  	info->shadow[BLK_RING_SIZE-1].req.u.rw.id = 0x0fffffff;
> @@ -2086,6 +2130,12 @@ static int __init xlblk_init(void)
>  {
>  	int ret;
>  
> +	if (xen_blkif_max_ring_pages > XENBUS_MAX_RING_PAGES) {
> +		pr_info("Invalid max_ring_pages (%d), will use default max: %d.\n",
> +			xen_blkif_max_ring_pages, XENBUS_MAX_RING_PAGES);
> +		xen_blkif_max_ring_pages = 1;
> +	}
> +
>  	if (!xen_domain())
>  		return -ENODEV;
>  
> 

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