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

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Message-ID: <1509555044.2530.35.camel@wdc.com>
Date:   Wed, 1 Nov 2017 16:50:45 +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 Mon, 2017-10-23 at 17:12 +0200, Roman Penyaev wrote:
> On Fri, Oct 20, 2017 at 10:05 PM, Bart Van Assche wrote:
> > Commit 6d8c6c0f97ad is something I came up with to fix queue lockups in the
> > SCSI and dm-mq drivers.
> 
> You mean fairness? (some hctx get less amount of chances to be restarted).
> That's why you need to restart them in RR fashion, right?

Commit 6d8c6c0f97ad not only improved fairness but also fixed a lockup scenario.
After a driver tag has been freed not only the hw queues of the request queue for
which a request completed must be reexamined but also the hw queues associated
with the other request queues that share the same tag set.

Bart.