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, 29 Jul 2020 23:36:48 +0800 [thread overview]
Message-ID: <20200729153648.GA1698748@T590> (raw)
In-Reply-To: <965cf22eea98c00618570da8424d0d94@mail.gmail.com>
On Wed, Jul 29, 2020 at 10:55:22AM +0530, Kashyap Desai wrote:
> > On Tue, Jul 28, 2020 at 08:54:27AM +0100, John Garry wrote:
> > > On 24/07/2020 03:47, Ming Lei wrote:
> > > > On Thu, Jul 23, 2020 at 06:29:01PM +0100, John Garry wrote:
> > > > > > > As I see, since megaraid will have 1:1 mapping of CPU to hw
> > > > > > > queue, will there only ever possibly a single bit set in
> > > > > > > ctx_map? If so, it seems a waste to always check every sbitmap
> > > > > > > map. But adding logic for this may negate any possible gains.
> > > > > >
> > > > > > It really depends on min and max cpu id in the map, then sbitmap
> > > > > > depth can be reduced to (max - min + 1). I'd suggest to double
> > > > > > check that cost of sbitmap_any_bit_set() really matters.
> > > > >
> > > > > Hi Ming,
> > > > >
> > > > > I'm not sure that reducing the search range would help much, as we
> > > > > still need to load some indexes of map[], and at best this may be
> > > > > reduced from 2/3
> > > > > -> 1 elements, depending on nr_cpus.
> > > >
> > > > I believe you misunderstood my idea, and you have to think it from
> > > > implementation viewpoint.
> > > >
> > > > The only workable way is to store the min cpu id as 'offset' and set
> > > > the sbitmap depth as (max - min + 1), isn't it? Then the actual cpu
> > > > id can be figured out via 'offset' + nr_bit. And the whole indexes
> > > > are just spread on the actual depth. BTW, max & min is the max / min
> > > > cpu id in hctx->cpu_map. So we can improve not only on 1:1, and I
> > > > guess most of MQ cases can benefit from the change, since it
> shouldn't be
> > usual for one ctx_map to cover both 0 & nr_cpu_id - 1.
> > > >
> > > > Meantime, we need to allocate the sbitmap dynamically.
> > >
> > > OK, so dynamically allocating the sbitmap could be good. I was
> > > thinking previously that we still allocate for nr_cpus size, and
> > > search a limited range - but this would have heavier runtime overhead.
> > >
> > > So if you really think that this may have some value, then let me
> > > know, so we can look to take it forward.
> >
> > Forget to mention, the in-tree code has been this shape for long time,
> please
> > see sbitmap_resize() called from blk_mq_map_swqueue().
> >
> > Another update is that V4 of 'scsi: core: only re-run queue in
> > scsi_end_request() if device queue is busy' is quite hard to implement
> since
> > commit b4fd63f42647110c9 ("Revert "scsi: core: run queue if SCSI device
> > queue isn't ready and queue is idle").
>
> Ming -
>
> Update from my testing. I found only one case of IO stall. I can discuss
> this specific topic if you like to send separate patch. It is too much
> interleaved discussion in this thread.
>
> I noted you mentioned that V4 of 'scsi: core: only re-run queue in
> scsi_end_request() if device queue is busy' need underlying support of
> "scsi: core: run queue if SCSI device queue isn't ready and queue is idle"
> patch which is already reverted in mainline.
Right.
> Overall idea of running h/w queues conditionally in your patch " scsi:
> core: only re-run queue in scsi_end_request" is still worth. There can be
I agree.
> some race if we use this patch and for that you have concern. Am I
> correct. ?
If the patch of "scsi: core: run queue if SCSI device queue isn't ready and
queue is idle" is re-added, the approach should work. However, it looks a bit
complicated, and I was thinking if one simpler approach can be figured out.
>
> One of the race I found in my testing is fixed by below patch -
>
> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> index 54f9015..bcfd33a 100644
> --- a/block/blk-mq-sched.c
> +++ b/block/blk-mq-sched.c
> @@ -173,8 +173,10 @@ static int blk_mq_do_dispatch_ctx(struct
> blk_mq_hw_ctx *hctx)
> if (!sbitmap_any_bit_set(&hctx->ctx_map))
> break;
>
> - if (!blk_mq_get_dispatch_budget(hctx))
> + if (!blk_mq_get_dispatch_budget(hctx)) {
> + blk_mq_delay_run_hw_queue(hctx,
> BLK_MQ_BUDGET_DELAY);
> break;
> + }
Actually all hw queues need to be run, instead of this hctx, cause
the budget stuff is request queue wide.
>
> rq = blk_mq_dequeue_from_ctx(hctx, ctx);
> if (!rq) {
>
>
> In my test setup, I have your V3 'scsi: core: only re-run queue in
> scsi_end_request() if device queue is busy' rebased on 5.8 which does not
> have
> "scsi: core: run queue if SCSI device queue isn't ready and queue is idle"
> since it is already reverted in mainline.
If you added the above patch, I believe you can remove the run queue in
scsi_end_request() unconditionally. However, the delay run queue may
degrade io performance.
Actually the re-run queue in scsi_end_request() is only for dequeuing
request from sw/scheduler queue. And no such issue if request stays in
hctx->dispatch list.
>
> I have 24 SAS SSD and I reduced QD = 16 so that I hit budget contention
> frequently. I am running ioscheduler=none.
> If hctx0 has 16 IO inflight (All those IO will be posted to h/q queue
> directly). Next IO (17th IO) will see budget contention and it will be
> queued into s/w queue.
> It is expected that queue will be kicked from scsi_end_request. It is
> possible that one of the IO completed and it reduce sdev->device_busy,
> but it has not yet reach the code which will kicked the h/w queue.
> Releasing budget and restarting h/w queue is not atomic. At the same time,
> another IO (18th IO) from submission path get the budget and it will be
> posted from below path. This IO will reset sdev->restart and it will not
> allow h/w queue to be restarted from completion path. This will lead one
Maybe re-run queue is needed before resetting sdev->restart if sdev->restart is 1.
Thanks,
Ming
next prev parent reply other threads:[~2020-07-29 15:37 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 [this message]
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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