linux-kernel - Re: [PATCH] bfq: backport: update internal depth state when queue depth changes

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Message-ID: <20190510201855.GB14410@sasha-vm>
Date:   Fri, 10 May 2019 16:18:55 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Eric Wheeler <stable@...ts.ewheeler.net>
Cc:     Paolo Valente <paolo.valente@...aro.org>,
        Jens Axboe <axboe@...nel.dk>,
        "open list:BFQ I/O SCHEDULER" <linux-block@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Eric Wheeler <bfq@...ux.ewheeler.net>, stable@...r.kernel.org
Subject: Re: [PATCH] bfq: backport: update internal depth state when queue
 depth changes

On Fri, May 10, 2019 at 10:56:32AM -0700, Eric Wheeler wrote:
>From: Jens Axboe <axboe@...nel.dk>
>
>commit 77f1e0a52d26242b6c2dba019f6ebebfb9ff701e upstream
>
>A previous commit moved the shallow depth and BFQ depth map calculations
>to be done at init time, moving it outside of the hotter IO path. This
>potentially causes hangs if the users changes the depth of the scheduler
>map, by writing to the 'nr_requests' sysfs file for that device.
>
>Add a blk-mq-sched hook that allows blk-mq to inform the scheduler if
>the depth changes, so that the scheduler can update its internal state.
>
>Signed-off-by: Eric Wheeler <bfq@...ux.ewheeler.net>
>Tested-by: Kai Krakow <kai@...shome.de>
>Reported-by: Paolo Valente <paolo.valente@...aro.org>
>Fixes: f0635b8a416e ("bfq: calculate shallow depths at init time")
>Signed-off-by: Jens Axboe <axboe@...nel.dk>
>Cc: stable@...r.kernel.org

I wasn't clear on what was backported here, so I've queued the upstream
version on 4.19 and 4.14, it doesn't seem to be relevant to older
branches.

--
Thanks,
Sasha