From: Ming Lei <ming.lei@redhat.com>
To: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 0/5] Make SCSI device suspend work reliably
Date: Sat, 9 Sep 2017 18:39:00 +0800 [thread overview]
Message-ID: <20170909103859.GA29285@ming.t460p> (raw)
In-Reply-To: <20170908235226.26622-1-bart.vanassche@wdc.com>
Bart,
On Fri, Sep 08, 2017 at 04:52:21PM -0700, Bart Van Assche wrote:
> Hello Jens,
>
> Recently it was reported on the block layer mailing list that suspend
> does not work reliably neither for the legacy block layer nor for blk-mq.
What is the issue? Why is it not reliably? Please describe it clearly.
> The purpose of this patch series is to make device suspend work reliably
> without affecting the hot path significantly and without introducing any
> race conditions between request queue cleanup and blk_get_request().
If you mean the approach in my patchset, please say it clearly.
I replied you already, but I am happy to reply you again.
Looks you do not understand the root cause behind I/O hang
during suspend/resume reported by Oleksandr.
Let me explain it again:
- the issue is not suspend/resume only, it is about SCSI quiesce vs.
RQF_PREEMPT.
- when SCSI device is put into quiesce, only RQF_PREEMPT request is
allowed to dispatch to lld, and other requests can't be dispatched
successfully.
- so if requests pool are used up during SCSI quiesce, no request can
be allocated for RQF_PREEMPT and these requests can't be freed too,
so I/O hang is caused because the pool is often very limited, and
easy to be consumed up
Except for the suspend I/O hang reported by Oleksandr, we also have
other I/O hang related with SCSI quiesce, both belongs to the
same kind of issue.
I don't see the issue above addressed by this patchset, so maybe
you are trying to fix another PM specific issue(not reported by
Oleksandr), I am just confused.
So again, please describe the issue to be addressed clearly first!
--
Ming
next prev parent reply other threads:[~2017-09-09 10:39 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-08 23:52 [PATCH 0/5] Make SCSI device suspend work reliably Bart Van Assche
2017-09-08 23:52 ` [PATCH 1/5] percpu-refcount: Introduce percpu_ref_switch_to_atomic_nowait() Bart Van Assche
2017-09-11 8:42 ` Johannes Thumshirn
2017-09-11 16:10 ` Bart Van Assche
2017-09-11 13:13 ` Tejun Heo
2017-09-11 16:09 ` Bart Van Assche
2017-09-11 16:37 ` tj
2017-09-11 16:55 ` Bart Van Assche
2017-09-11 17:20 ` Tejun Heo
2017-09-11 17:29 ` Bart Van Assche
2017-09-08 23:52 ` [PATCH 2/5] scsi: Change the type of the second last argument of scsi_execute() Bart Van Assche
2017-09-08 23:52 ` [PATCH 3/5] block: Introduce REQ_PM and remove RQF_PM Bart Van Assche
2017-09-08 23:52 ` [PATCH 4/5] block: Make SCSI device suspend work reliably Bart Van Assche
2017-09-12 2:29 ` Ming Lei
2017-09-12 15:45 ` Bart Van Assche
2017-09-12 16:10 ` Ming Lei
2017-09-12 16:25 ` Ming Lei
2017-09-08 23:52 ` [PATCH 5/5] blk-mq: Implement power management support Bart Van Assche
2017-09-12 9:14 ` Ming Lei
2017-09-09 10:39 ` Ming Lei [this message]
2017-09-11 16:25 ` [PATCH 0/5] Make SCSI device suspend work reliably Bart Van Assche
2017-09-12 2:17 ` Ming Lei
-- strict thread matches above, loose matches on Subject: below --
2017-09-09 14:35 Oleksandr Natalenko
2017-09-11 17:31 ` Bart Van Assche
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