From: Ming Lei <ming.lei@redhat.com>
To: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: John Garry <john.garry@huawei.com>,
linux-block@vger.kernel.org, linux-scsi@vger.kernel.org,
"Martin K. Petersen" <martin.petersen@oracle.com>,
Jens Axboe <axboe@kernel.dk>,
Douglas Gilbert <dgilbert@interlog.com>
Subject: Re: [bug report] shared tags causes IO hang and performance drop
Date: Thu, 15 Apr 2021 08:58:21 +0800 [thread overview]
Message-ID: <YHePrQluaOJG/P8w@T590> (raw)
In-Reply-To: <b41586781cffea03c5fd6b0849e2b9e4@mail.gmail.com>
On Wed, Apr 14, 2021 at 07:29:07PM +0530, Kashyap Desai wrote:
> > > I tried both - 5.12.0-rc1 and 5.11.0-rc2+ and there is a same
> behavior.
> > > Let me also check megaraid_sas and see if anything generic or this is
> > > a special case of scsi_debug.
> >
> > As I mentioned, it could be one generic issue wrt. SCHED_RESTART.
> > shared tags might have to restart all hctx since all share same tags.
>
> Ming - I tried many combination on MR shared host tag driver but there is
> no single instance of IO hang.
> I will keep trying, but when I look at scsi_debug driver code I found
> below odd settings in scsi_debug driver.
> can_queue of adapter is set to 128 but queue_depth of sdev is set to 255.
>
> If I apply below patch, scsi_debug driver's hang is also resolved. Ideally
> sdev->queue depth cannot exceed shost->can_queue.
> Not sure why cmd_per_lun is 255 in scsi_debug driver which can easily
> exceed can_queue. I will simulate something similar in MR driver and see
> how it behaves w.r.t IO hang issue.
>
> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
> index 70165be10f00..dded762540ee 100644
> --- a/drivers/scsi/scsi_debug.c
> +++ b/drivers/scsi/scsi_debug.c
> @@ -218,7 +218,7 @@ static const char *sdebug_version_date = "20200710";
> */
> #define SDEBUG_CANQUEUE_WORDS 3 /* a WORD is bits in a long */
> #define SDEBUG_CANQUEUE (SDEBUG_CANQUEUE_WORDS * BITS_PER_LONG)
> -#define DEF_CMD_PER_LUN 255
> +#define DEF_CMD_PER_LUN SDEBUG_CANQUEUE
>
> /* UA - Unit Attention; SA - Service Action; SSU - Start Stop Unit */
> #define F_D_IN 1 /* Data-in command (e.g. READ) */
> @@ -7558,6 +7558,7 @@ static int sdebug_driver_probe(struct device *dev)
> sdbg_host = to_sdebug_host(dev);
>
> sdebug_driver_template.can_queue = sdebug_max_queue;
> + sdebug_driver_template.cmd_per_lun = sdebug_max_queue;
> if (!sdebug_clustering)
> sdebug_driver_template.dma_boundary = PAGE_SIZE - 1;
Yeah, the change makes the issue disappear. That looks scsi's restart
(scsi_run_queue_async<-scsi_end_request) finally restarts the queue.
Thanks,
Ming
prev parent reply other threads:[~2021-04-15 0:58 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-14 7:50 [bug report] shared tags causes IO hang and performance drop Ming Lei
2021-04-14 10:10 ` John Garry
2021-04-14 10:38 ` Ming Lei
2021-04-14 10:42 ` Kashyap Desai
2021-04-14 11:12 ` Ming Lei
2021-04-14 12:06 ` John Garry
2021-04-15 3:46 ` Ming Lei
2021-04-15 10:41 ` John Garry
2021-04-15 12:18 ` Ming Lei
2021-04-15 15:41 ` John Garry
2021-04-16 0:46 ` Ming Lei
2021-04-16 8:29 ` John Garry
2021-04-16 8:39 ` Ming Lei
2021-04-16 14:59 ` John Garry
2021-04-20 3:06 ` Douglas Gilbert
2021-04-20 3:22 ` Bart Van Assche
2021-04-20 4:54 ` Douglas Gilbert
2021-04-20 6:52 ` Ming Lei
2021-04-20 20:22 ` Douglas Gilbert
2021-04-21 1:40 ` Ming Lei
2021-04-23 8:43 ` John Garry
2021-04-26 10:53 ` John Garry
2021-04-26 14:48 ` Ming Lei
2021-04-26 15:52 ` John Garry
2021-04-26 16:03 ` Ming Lei
2021-04-26 17:02 ` John Garry
2021-04-26 23:59 ` Ming Lei
2021-04-27 7:52 ` John Garry
2021-04-27 9:11 ` Ming Lei
2021-04-27 9:37 ` John Garry
2021-04-27 9:52 ` Ming Lei
2021-04-27 10:15 ` John Garry
2021-07-07 17:06 ` John Garry
2021-04-14 13:59 ` Kashyap Desai
2021-04-14 17:03 ` Douglas Gilbert
2021-04-14 18:19 ` John Garry
2021-04-14 19:39 ` Douglas Gilbert
2021-04-15 0:58 ` Ming Lei [this message]
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