From: Kashyap Desai <kashyap.desai@broadcom.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: John Garry <john.garry@huawei.com>,
axboe@kernel.dk, jejb@linux.ibm.com, martin.petersen@oracle.com,
don.brace@microsemi.com, Sumit Saxena <sumit.saxena@broadcom.com>,
bvanassche@acm.org, hare@suse.com, hch@lst.de,
Shivasharan Srikanteshwara
<shivasharan.srikanteshwara@broadcom.com>,
linux-block@vger.kernel.org, linux-scsi@vger.kernel.org,
esc.storagedev@microsemi.com, chenxiang66@hisilicon.com,
"PDL,MEGARAIDLINUX" <megaraidlinux.pdl@broadcom.com>
Subject: RE: [PATCH RFC v7 10/12] megaraid_sas: switch fusion adapters to MQ
Date: Thu, 6 Aug 2020 15:55:50 +0530 [thread overview]
Message-ID: <5adffdf805179428bdd0dd6c293a4f7d@mail.gmail.com> (raw)
In-Reply-To: <20200805084031.GA1995289@T590>
> > Ming -
> >
> > I noted your comments.
> >
> > I have completed testing and this particular latest performance issue
> > on Volume is outstanding.
> > Currently it is 20-25% performance drop in IOPs and we want that to be
> > closed before shared host tag is enabled for <megaraid_sas> driver.
> > Just for my understanding - What will be the next steps on this ?
> >
> > I can validate any new approach/patch for this issue.
> >
>
> Hello,
>
> What do you think of the following patch?
I tested this patch. I still see IO hang.
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index
> c866a4f33871..49f0fc5c7a63 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -552,8 +552,24 @@ static void scsi_run_queue_async(struct scsi_device
> *sdev)
> if (scsi_target(sdev)->single_lun ||
> !list_empty(&sdev->host->starved_list))
> kblockd_schedule_work(&sdev->requeue_work);
> - else
> - blk_mq_run_hw_queues(sdev->request_queue, true);
> + else {
> + /*
> + * smp_mb() implied in either rq->end_io or
> blk_mq_free_request
> + * is for ordering writing .device_busy in
scsi_device_unbusy()
> + * and reading sdev->restarts.
> + */
> + int old = atomic_read(&sdev->restarts);
> +
> + if (old) {
> + blk_mq_run_hw_queues(sdev->request_queue, true);
> +
> + /*
> + * ->restarts has to be kept as non-zero if there
is
> + * new budget contention comes.
> + */
> + atomic_cmpxchg(&sdev->restarts, old, 0);
> + }
> + }
> }
>
> /* Returns false when no more bytes to process, true if there are more
*/
> @@ -1612,8 +1628,34 @@ static void scsi_mq_put_budget(struct
> request_queue *q) static bool scsi_mq_get_budget(struct request_queue
*q)
> {
> struct scsi_device *sdev = q->queuedata;
> + int ret = scsi_dev_queue_ready(q, sdev);
>
> - return scsi_dev_queue_ready(q, sdev);
> + if (ret)
> + return true;
> +
> + /*
> + * If all in-flight requests originated from this LUN are
completed
> + * before setting .restarts, sdev->device_busy will be observed as
> + * zero, then blk_mq_delay_run_hw_queue() will dispatch this
request
> + * soon. Otherwise, completion of one of these request will
observe
> + * the .restarts flag, and the request queue will be run for
handling
> + * this request, see scsi_end_request().
> + */
> + atomic_inc(&sdev->restarts);
> +
> + /*
> + * Order writing .restarts and reading .device_busy, and make sure
> + * .restarts is visible to scsi_end_request(). Its pair is implied
by
> + * __blk_mq_end_request() in scsi_end_request() for ordering
> + * writing .device_busy in scsi_device_unbusy() and reading
.restarts.
> + *
> + */
> + smp_mb__after_atomic();
> +
> + if (unlikely(atomic_read(&sdev->device_busy) == 0 &&
> + !scsi_device_blocked(sdev)))
> + blk_mq_delay_run_hw_queues(sdev->request_queue,
> SCSI_QUEUE_DELAY);
Hi Ming -
There is still some race which is not handled. Take a case of IO is not
able to get budget and it has already marked <restarts> flag.
<restarts> flag will be seen non-zero in completion path and completion
path will attempt h/w queue run. (But this particular IO is still not in
s/w queue.).
Attempt of running h/w queue from completion path will not flush any IO
since there is no IO in s/w queue.
I think above code is added assuming it should manage this particular
case, but this code also does not help. If some IO in between submitted
directly to the h/w queue then sdev->device_busy will be non-zero.
If I move above section of the code into completion path, IO hang is
resolved. I also verify performance -
Multi Drive R0 1 workers per VD gives 662K prior to this patch and now
It scale to 1.1M IOPs. (90% improvement)
Multi Drive R0 4 workers per VD gives 1.9M prior to this patch and now It
scale to 3.1M IOPs. (50% improvement)
Here is modified patch -
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 6f50e5c..dcdc5f6 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -594,8 +594,26 @@ static bool scsi_end_request(struct request *req,
blk_status_t error,
if (scsi_target(sdev)->single_lun ||
!list_empty(&sdev->host->starved_list))
kblockd_schedule_work(&sdev->requeue_work);
- else
- blk_mq_run_hw_queues(q, true);
+ else {
+ /*
+ * smp_mb() implied in either rq->end_io or
blk_mq_free_request
+ * is for ordering writing .device_busy in
scsi_device_unbusy()
+ * and reading sdev->restarts.
+ */
+ int old = atomic_read(&sdev->restarts);
+
+ if (old) {
+ blk_mq_run_hw_queues(sdev->request_queue, true);
+
+ /*
+ * ->restarts has to be kept as non-zero if there
is
+ * new budget contention comes.
+ */
+ atomic_cmpxchg(&sdev->restarts, old, 0);
+ } else if (unlikely(atomic_read(&sdev->device_busy) == 0
&&
+ !scsi_device_blocked(sdev)))
+ blk_mq_delay_run_hw_queues(sdev->request_queue,
SCSI_QUEUE_DELAY);
+ }
percpu_ref_put(&q->q_usage_counter);
return false;
@@ -1615,8 +1633,31 @@ static bool scsi_mq_get_budget(struct blk_mq_hw_ctx
*hctx)
{
struct request_queue *q = hctx->queue;
struct scsi_device *sdev = q->queuedata;
+ int ret = scsi_dev_queue_ready(q, sdev);
+
+ if (ret)
+ return true;
- return scsi_dev_queue_ready(q, sdev);
+ /*
+ * If all in-flight requests originated from this LUN are
completed
+ * before setting .restarts, sdev->device_busy will be observed as
+ * zero, then blk_mq_delay_run_hw_queue() will dispatch this
request
+ * soon. Otherwise, completion of one of these request will
observe
+ * the .restarts flag, and the request queue will be run for
handling
+ * this request, see scsi_end_request().
+ */
+ atomic_inc(&sdev->restarts);
+
+ /*
+ * Order writing .restarts and reading .device_busy, and make sure
+ * .restarts is visible to scsi_end_request(). Its pair is implied
by
+ * __blk_mq_end_request() in scsi_end_request() for ordering
+ * writing .device_busy in scsi_device_unbusy() and reading
.restarts.
+ *
+ */
+ smp_mb__after_atomic();
+
+ return false;
}
static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index bc59090..ac45058 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -108,7 +108,8 @@ struct scsi_device {
atomic_t device_busy; /* commands actually active on
LLDD */
atomic_t device_blocked; /* Device returned QUEUE_FULL. */
-
+
+ atomic_t restarts;
spinlock_t list_lock;
struct list_head starved_entry;
unsigned short queue_depth; /* How deep of a queue we want */
next prev parent reply other threads:[~2020-08-06 11:17 UTC|newest]
Thread overview: 123+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-10 17:29 [PATCH RFC v7 00/12] blk-mq/scsi: Provide hostwide shared tags for SCSI HBAs John Garry
2020-06-10 17:29 ` [PATCH RFC v7 01/12] blk-mq: rename BLK_MQ_F_TAG_SHARED as BLK_MQ_F_TAG_QUEUE_SHARED John Garry
2020-06-10 17:29 ` [PATCH RFC v7 02/12] blk-mq: rename blk_mq_update_tag_set_depth() John Garry
2020-06-11 2:57 ` Ming Lei
2020-06-11 8:26 ` John Garry
2020-06-23 11:25 ` John Garry
2020-06-23 14:23 ` Hannes Reinecke
2020-06-24 8:13 ` Kashyap Desai
2020-06-29 16:18 ` John Garry
2020-08-10 16:51 ` Kashyap Desai
2020-08-11 8:01 ` John Garry
2020-08-11 16:34 ` Kashyap Desai
2020-06-10 17:29 ` [PATCH RFC v7 03/12] blk-mq: Use pointers for blk_mq_tags bitmap tags John Garry
2020-06-10 17:29 ` [PATCH RFC v7 04/12] blk-mq: Facilitate a shared sbitmap per tagset John Garry
2020-06-11 3:37 ` Ming Lei
2020-06-11 10:09 ` John Garry
2020-06-10 17:29 ` [PATCH RFC v7 05/12] blk-mq: Record nr_active_requests per queue for when using shared sbitmap John Garry
2020-06-11 4:04 ` Ming Lei
2020-06-11 10:22 ` John Garry
2020-06-10 17:29 ` [PATCH RFC v7 06/12] blk-mq: Record active_queues_shared_sbitmap per tag_set " John Garry
2020-06-11 13:16 ` Hannes Reinecke
2020-06-11 14:22 ` John Garry
2020-06-10 17:29 ` [PATCH RFC v7 07/12] blk-mq: Add support in hctx_tags_bitmap_show() for a " John Garry
2020-06-11 13:19 ` Hannes Reinecke
2020-06-11 14:33 ` John Garry
2020-06-12 6:06 ` Hannes Reinecke
2020-06-29 15:32 ` About sbitmap_bitmap_show() and cleared bits (was Re: [PATCH RFC v7 07/12] blk-mq: Add support in hctx_tags_bitmap_show() for a shared sbitmap) John Garry
2020-06-30 6:33 ` Hannes Reinecke
2020-06-30 7:30 ` John Garry
2020-06-30 11:36 ` John Garry
2020-06-30 14:55 ` Bart Van Assche
2020-07-13 9:41 ` [PATCH RFC v7 07/12] blk-mq: Add support in hctx_tags_bitmap_show() for a shared sbitmap John Garry
2020-07-13 12:20 ` Hannes Reinecke
2020-06-10 17:29 ` [PATCH RFC v7 08/12] scsi: Add template flag 'host_tagset' John Garry
2020-06-10 17:29 ` [PATCH RFC v7 09/12] scsi: hisi_sas: Switch v3 hw to MQ John Garry
2020-06-10 17:29 ` [PATCH RFC v7 10/12] megaraid_sas: switch fusion adapters " John Garry
2020-07-02 10:23 ` Kashyap Desai
2020-07-06 8:23 ` John Garry
2020-07-06 8:45 ` Hannes Reinecke
2020-07-06 9:26 ` John Garry
2020-07-06 9:40 ` Hannes Reinecke
2020-07-06 19:19 ` Kashyap Desai
2020-07-07 7:58 ` John Garry
2020-07-07 14:45 ` Kashyap Desai
2020-07-07 16:17 ` John Garry
2020-07-09 19:01 ` Kashyap Desai
2020-07-10 8:10 ` John Garry
2020-07-13 7:55 ` Kashyap Desai
2020-07-13 8:42 ` John Garry
2020-07-19 19:07 ` Kashyap Desai
2020-07-20 7:23 ` Kashyap Desai
2020-07-20 9:18 ` John Garry
2020-07-21 1:13 ` Ming Lei
2020-07-21 6:53 ` Kashyap Desai
2020-07-22 4:12 ` Ming Lei
2020-07-22 5:30 ` Kashyap Desai
2020-07-22 8:04 ` Ming Lei
2020-07-22 9:32 ` John Garry
2020-07-23 14:07 ` Ming Lei
2020-07-23 17:29 ` John Garry
2020-07-24 2:47 ` Ming Lei
2020-07-28 7:54 ` John Garry
2020-07-28 8:45 ` Ming Lei
2020-07-29 5:25 ` Kashyap Desai
2020-07-29 15:36 ` Ming Lei
2020-07-29 18:31 ` Kashyap Desai
2020-08-04 8:36 ` Ming Lei
2020-08-04 9:27 ` Kashyap Desai
2020-08-05 8:40 ` Ming Lei
2020-08-06 10:25 ` Kashyap Desai [this message]
2020-08-06 13:38 ` Ming Lei
2020-08-06 14:37 ` Kashyap Desai
2020-08-06 15:29 ` Ming Lei
2020-08-08 19:05 ` Kashyap Desai
2020-08-09 2:16 ` Ming Lei
2020-08-10 16:38 ` Kashyap Desai
2020-08-11 8:09 ` John Garry
2020-08-04 17:00 ` John Garry
2020-08-05 2:56 ` Ming Lei
2020-07-28 8:01 ` Kashyap Desai
2020-07-08 11:31 ` John Garry
2020-06-10 17:29 ` [PATCH RFC v7 11/12] smartpqi: enable host tagset John Garry
2020-07-14 13:16 ` John Garry
2020-07-14 13:31 ` John Garry
2020-07-14 18:16 ` Don.Brace
2020-07-15 7:28 ` John Garry
2020-07-14 14:02 ` Hannes Reinecke
2020-08-18 8:33 ` John Garry
2020-06-10 17:29 ` [PATCH RFC v7 12/12] hpsa: enable host_tagset and switch to MQ John Garry
2020-07-14 7:37 ` John Garry
2020-07-14 7:41 ` Hannes Reinecke
2020-07-14 7:52 ` John Garry
2020-07-14 8:06 ` Ming Lei
2020-07-14 9:53 ` John Garry
2020-07-14 10:14 ` Ming Lei
2020-07-14 10:43 ` Hannes Reinecke
2020-07-14 10:19 ` Hannes Reinecke
2020-07-14 10:35 ` John Garry
2020-07-14 10:44 ` Ming Lei
2020-07-14 10:52 ` John Garry
2020-07-14 12:04 ` Ming Lei
2020-08-03 20:39 ` Don.Brace
2020-08-04 9:27 ` John Garry
2020-08-04 15:18 ` Don.Brace
2020-08-05 11:21 ` John Garry
2020-08-14 21:04 ` Don.Brace
2020-08-17 8:00 ` John Garry
2020-08-17 18:39 ` Don.Brace
2020-08-18 7:14 ` Hannes Reinecke
2020-07-16 16:14 ` Don.Brace
2020-07-16 19:45 ` Don.Brace
2020-07-17 10:11 ` John Garry
2020-06-11 3:07 ` [PATCH RFC v7 00/12] blk-mq/scsi: Provide hostwide shared tags for SCSI HBAs Ming Lei
2020-06-11 9:35 ` John Garry
2020-06-12 18:47 ` Kashyap Desai
2020-06-15 2:13 ` Ming Lei
2020-06-15 6:57 ` Kashyap Desai
2020-06-16 1:00 ` Ming Lei
2020-06-17 11:26 ` Kashyap Desai
2020-06-22 6:24 ` Hannes Reinecke
2020-06-23 0:55 ` Ming Lei
2020-06-23 11:50 ` Kashyap Desai
2020-06-23 12:11 ` Kashyap Desai
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