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: Wed, 22 Jul 2020 16:04:09 +0800 [thread overview]
Message-ID: <20200722080409.GB912316@T590> (raw)
In-Reply-To: <f6f05483491c391ce79486b8fb78cb2e@mail.gmail.com>
On Wed, Jul 22, 2020 at 11:00:45AM +0530, Kashyap Desai wrote:
> > On Tue, Jul 21, 2020 at 12:23:39PM +0530, Kashyap Desai wrote:
> > > > > >
> > > > > > Perf top (shared host tag. IOPS = 230K)
> > > > > >
> > > > > > 13.98% [kernel] [k] sbitmap_any_bit_set
> > > > > > 6.43% [kernel] [k] blk_mq_run_hw_queue
> > > > >
> > > > > blk_mq_run_hw_queue function take more CPU which is called from "
> > > > > scsi_end_request"
> > > >
> > > > The problem could be that nr_hw_queues is increased a lot so that
> > > > sample
> > > on
> > > > blk_mq_run_hw_queue() can be observed now.
> > >
> > > Yes. That is correct.
> > >
> > > >
> > > > > It looks like " blk_mq_hctx_has_pending" handles only elevator
> > > > > (scheduler) case. If queue has ioscheduler=none, we can skip. I
> > > > > case of scheduler=none, IO will be pushed to hardware queue and it
> > > > > by pass
> > > > software queue.
> > > > > Based on above understanding, I added below patch and I can see
> > > > > performance scale back to expectation.
> > > > >
> > > > > Ming mentioned that - we cannot remove blk_mq_run_hw_queues()
> > from
> > > > > IO completion path otherwise we may see IO hang. So I have just
> > > > > modified completion path assuming it is only required for IO
> scheduler
> > case.
> > > > > https://www.spinics.net/lists/linux-block/msg55049.html
> > > > >
> > > > > Please review and let me know if this is good or we have to
> > > > > address with proper fix.
> > > > >
> > > > > diff --git a/block/blk-mq.c b/block/blk-mq.c index
> > > > > 1be7ac5a4040..b6a5b41b7fc2 100644
> > > > > --- a/block/blk-mq.c
> > > > > +++ b/block/blk-mq.c
> > > > > @@ -1559,6 +1559,9 @@ void blk_mq_run_hw_queues(struct
> > > > request_queue
> > > > > *q, bool async)
> > > > > struct blk_mq_hw_ctx *hctx;
> > > > > int i;
> > > > >
> > > > > + if (!q->elevator)
> > > > > + return;
> > > > > +
> > > >
> > > > This way shouldn't be correct, blk_mq_run_hw_queues() is still
> > > > needed
> > > for
> > > > none because request may not be dispatched successfully by direct
> issue.
> > >
> > > When block layer attempt posting request to h/w queue directly (for
> > > ioscheduler=none) and if it fails, it is calling
> > > blk_mq_request_bypass_insert().
> > > blk_mq_request_bypass_insert function will start the h/w queue from
> > > submission context. Do we still have an issue if we skip running hw
> > > queue from completion ?
> >
> > The thing is that we can't guarantee that direct issue or adding request
> into
> > hctx->dispatch is always done for MQ/none, for example, request still
> > can be added to sw queue from blk_mq_flush_plug_list() when mq plug is
> > applied.
>
> I see even blk_mq_sched_insert_requests() from blk_mq_flush_plug_list make
> sure it run the h/w queue. If all the submission path which deals with s/w
> queue make sure they run h/w queue, can't we remove blk_mq_run_hw_queues()
> from scsi_end_request ?
No, one purpose of blk_mq_run_hw_queues() is for rerun queue in case that
dispatch budget is running out of in submission path, and sdev->device_busy is
shared by all hw queues on this scsi device.
I posted one patch for avoiding it in scsi_end_request() before, looks it
never lands upstream:
https://lore.kernel.org/linux-block/20191118100640.3673-1-ming.lei@redhat.com/
Thanks,
Ming
next prev parent reply other threads:[~2020-07-22 8:04 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 [this message]
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
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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