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Message-ID: <1374885793.7397.1537.camel@haakon3.risingtidesystems.com>
Date: Fri, 26 Jul 2013 17:43:13 -0700
From: "Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To: Jens Axboe <axboe@...nel.dk>
Cc: Alexander Gordeev <agordeev@...hat.com>,
James Bottomley <James.Bottomley@...senPartnership.com>,
Mike Christie <michaelc@...wisc.edu>,
Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
linux-ide@...r.kernel.org, Jeff Garzik <jgarzik@...ox.com>,
linux-scsi <linux-scsi@...r.kernel.org>
Subject: Re: [PATCH RESEND 0/1] AHCI: Optimize interrupt processing
On Fri, 2013-07-26 at 14:14 -0700, Nicholas A. Bellinger wrote:
> On Thu, 2013-07-25 at 20:09 -0600, Jens Axboe wrote:
> > On Thu, Jul 25 2013, Nicholas A. Bellinger wrote:
> > > On Thu, 2013-07-25 at 12:16 +0200, Alexander Gordeev wrote:
> > > > On Mon, Jul 22, 2013 at 02:10:36PM -0700, Nicholas A. Bellinger wrote:
> > > > > Np. FYI, you'll want to use the latest commit e7827b351 HEAD from
> > > > > target-pending/scsi-mq, which now has functioning scsi-generic support.
> > > >
> > > > Survives a boot, a kernel build and the build's result :)
> > >
> > > Great. Thanks for the feedback Alexander!
> > >
> > > So the next step on my end is to enable -mq for ahci, and verify initial
> > > correctness using QEMU/KVM hardware emulation.
> > >
> > > Btw, I've been looking at enabling the SHT->cmd_size for struct
> > > ata_queued_cmd descriptor pre-allocation, but AFAICT these descriptors
> > > are already all pre-allocated by libata and obtained via ata_qc_new() ->
> > > __ata_qc_from_tag() during ata_scsi_queuecmd().
> >
> > Might still not be a bad idea to do it:
> >
> > - Cleans up a driver, getting rid of the need to alloc, maintain, and
> > free those structures.
> >
> > - Should be some cache locality benefits to having it all sequential.
> >
>
> Looking at this some more, there are a number of locations outside of
> the main blk_mq_ops->queue_rq() -> SHT->queuecommand_mq() dispatch that
> use *ata_qc_from_tag() to obtain *ata_queued_cmd, and a few without a
> associated struct scsi_cmnd like libata-core.c:ata_exec_internal_sg()
> for example..
>
> So I don't think (completely) getting rid of ata_port->qcmds[] will be
> possible, and just converting the ata_scsi_queuecmd() path to use the
> extra SHT->cmd_size pre-allocation for *ata_queued_cmd might end up
> being more trouble that it's worth. Still undecided on that part..
>
> Tejun, do you have any thoughts + input here..?
>
OK, so I decided to give this a shot anyways.. Here is a quick
conversion for libata + AHCI to use blk-mq -> scsi-mq pre-allocation for
ata_queued_cmd descriptors:
diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 2b50dfd..61b3db8 100644
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -92,6 +92,9 @@ static int ahci_pci_device_resume(struct pci_dev *pdev);
static struct scsi_host_template ahci_sht = {
AHCI_SHT("ahci"),
+ .scsi_mq = true,
+ .cmd_size = sizeof(struct ata_queued_cmd),
+ .queuecommand_mq = ata_scsi_queuecmd,
};
diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index f218427..e21814d 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -4725,29 +4725,25 @@ void swap_buf_le16(u16 *buf, unsigned int buf_words)
/**
* ata_qc_new - Request an available ATA command, for queueing
* @ap: target port
+ * @sc: incoming scsi_cmnd descriptor
*
* LOCKING:
* None.
*/
-static struct ata_queued_cmd *ata_qc_new(struct ata_port *ap)
+static struct ata_queued_cmd *ata_qc_new(struct ata_port *ap,
+ struct scsi_cmnd *sc)
{
struct ata_queued_cmd *qc = NULL;
- unsigned int i;
+ struct request *rq = sc->request;
/* no command while frozen */
if (unlikely(ap->pflags & ATA_PFLAG_FROZEN))
return NULL;
- /* the last tag is reserved for internal command. */
- for (i = 0; i < ATA_MAX_QUEUE - 1; i++)
- if (!test_and_set_bit(i, &ap->qc_allocated)) {
- qc = __ata_qc_from_tag(ap, i);
- break;
- }
-
- if (qc)
- qc->tag = i;
+ qc = (struct ata_queued_cmd *)sc->SCp.ptr;
+ qc->scsicmd = sc;
+ qc->tag = rq->tag;
return qc;
}
@@ -4755,19 +4751,20 @@ static struct ata_queued_cmd *ata_qc_new(struct ata_port *ap)
/**
* ata_qc_new_init - Request an available ATA command, and initialize it
* @dev: Device from whom we request an available command structure
+ * @sc: incoming scsi_cmnd descriptor
*
* LOCKING:
* None.
*/
-struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev)
+struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev,
+ struct scsi_cmnd *sc)
{
struct ata_port *ap = dev->link->ap;
struct ata_queued_cmd *qc;
- qc = ata_qc_new(ap);
+ qc = ata_qc_new(ap, sc);
if (qc) {
- qc->scsicmd = NULL;
qc->ap = ap;
qc->dev = dev;
@@ -4797,10 +4794,9 @@ void ata_qc_free(struct ata_queued_cmd *qc)
qc->flags = 0;
tag = qc->tag;
- if (likely(ata_tag_valid(tag))) {
+
+ if (likely(ata_tag_valid(tag)))
qc->tag = ATA_TAG_POISON;
- clear_bit(tag, &ap->qc_allocated);
- }
}
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 0101af5..e5ab880 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -742,9 +742,8 @@ static struct ata_queued_cmd *ata_scsi_qc_new(struct ata_device *dev,
{
struct ata_queued_cmd *qc;
- qc = ata_qc_new_init(dev);
+ qc = ata_qc_new_init(dev, cmd);
if (qc) {
- qc->scsicmd = cmd;
qc->scsidone = cmd->scsi_done;
qc->sg = scsi_sglist(cmd);
diff --git a/drivers/ata/libata.h b/drivers/ata/libata.h
index c949dd3..4cd88af 100644
--- a/drivers/ata/libata.h
+++ b/drivers/ata/libata.h
@@ -63,7 +63,8 @@ extern struct ata_link *ata_dev_phys_link(struct ata_device *dev);
extern void ata_force_cbl(struct ata_port *ap);
extern u64 ata_tf_to_lba(const struct ata_taskfile *tf);
extern u64 ata_tf_to_lba48(const struct ata_taskfile *tf);
-extern struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev);
+extern struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev,
+ struct scsi_cmnd *sc);
extern int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
u64 block, u32 n_block, unsigned int tf_flags,
unsigned int tag);
diff --git a/include/linux/libata.h b/include/linux/libata.h
index eae7a05..52e9e9e 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -35,9 +35,13 @@
#include <linux/ata.h>
#include <linux/workqueue.h>
#include <scsi/scsi_host.h>
+#include <scsi/scsi_device.h>
+#include <scsi/scsi_cmnd.h>
#include <linux/acpi.h>
#include <linux/cdrom.h>
#include <linux/sched.h>
+#include <linux/blk-mq.h>
+#include <../../block/blk-mq.h>
/*
* Define if arch has non-standard setup. This is a _PCI_ standard
@@ -1500,9 +1504,26 @@ static inline void ata_qc_set_polling(struct ata_queued_cmd *qc)
static inline struct ata_queued_cmd *__ata_qc_from_tag(struct ata_port *ap,
unsigned int tag)
{
- if (likely(ata_tag_valid(tag)))
- return &ap->qcmd[tag];
- return NULL;
+ struct scsi_device *sdev = ap->link.device[0].sdev;
+ struct request_queue *q = sdev->request_queue;
+
+ if (unlikely(!ata_tag_valid(tag)))
+ return NULL;
+
+ if (likely(sdev->host->hostt->scsi_mq)) {
+ struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
+ struct blk_mq_hw_ctx *hctx = q->mq_ops->map_queue(q, ctx->cpu);
+ struct request *rq;
+ struct ata_queued_cmd *qc;
+
+ BUG_ON(tag > hctx->queue_depth);
+
+ rq = hctx->rqs[tag];
+ qc = blk_mq_rq_to_pdu(rq) + sizeof(struct scsi_cmnd);
+ blk_mq_put_ctx(ctx);
+ return qc;
+ }
+ return &ap->qcmd[tag];
}
The thing that I'm hung up on now for existing __ata_qc_from_tag() usage
outside of the main blk_mq_ops->queue_rq -> SHT->queuecommand_mq()
dispatch path, is how to actually locate the underlying scsi_device ->
request_queue -> blk_mq_ctx -> blk_mq_hw_hctx from the passed
ata_port..?
Considering there can be more than a single ata_device hanging off each
ata_port, the '*sdev = ap->link.device[0].sdev' in __ata_qc_from_tag()
is definitely bogus, but I'm not sure how else to correlate
blk-mq/scsi-mq per device descriptors to existing code expecting
ata_port->qcmd[] descriptors to be shared across multiple devices..
Tejun..?
--nab
--
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