linux-kernel - Re: [PATCH 1/1] [RFC] blk-mq: fix queue stalling on shared hctx restart

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Message-ID: <1508529929.3029.20.camel@wdc.com>
Date:   Fri, 20 Oct 2017 20:05:30 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "roman.penyaev@...fitbricks.com" <roman.penyaev@...fitbricks.com>
CC:     "hch@....de" <hch@....de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "hare@...e.com" <hare@...e.com>, "axboe@...com" <axboe@...com>
Subject: Re: [PATCH 1/1] [RFC] blk-mq: fix queue stalling on shared hctx
 restart

On Fri, 2017-10-20 at 11:39 +0200, Roman Penyaev wrote:
> But what bothers me is these looong loops inside blk_mq_sched_restart(),
> and since you are the author of the original 6d8c6c0f97ad ("blk-mq: Restart
> a single queue if tag sets are shared") I want to ask what was the original
> problem which you attempted to fix?  Likely I am missing some test scenario
> which would be great to know about.

Long loops? How many queues share the same tag set on your setup? How many
hardware queues does your block driver create per request queue?

Commit 6d8c6c0f97ad is something I came up with to fix queue lockups in the
SCSI and dm-mq drivers.

Bart.