From: Ming Lei <ming.lei@redhat.com>
To: Kashyap Desai <kashyap.desai@broadcom.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 21:38:19 +0800 [thread overview]
Message-ID: <20200806133819.GA2046861@T590> (raw)
In-Reply-To: <5adffdf805179428bdd0dd6c293a4f7d@mail.gmail.com>
On Thu, Aug 06, 2020 at 03:55:50PM +0530, Kashyap Desai wrote:
> > > 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.
Then where is the IO to be submitted in case of running out of budget?
Any IO request which is going to be added to hctx->dispatch, the queue will be
re-run via blk-mq core.
Any IO request being issued directly when running out of budget will be
insert to hctx->dispatch or sw/scheduler queue, will be run in the
submission path.
Thanks,
Ming
next prev parent reply other threads:[~2020-08-06 17:11 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
2020-08-06 13:38 ` Ming Lei [this message]
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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