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

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Message-ID: <alpine.LRH.2.11.1905102312220.4789@mx.ewheeler.net>
Date:   Fri, 10 May 2019 23:17:20 +0000 (UTC)
From:   Eric Wheeler <stable@...ts.ewheeler.net>
To:     Sasha Levin <sashal@...nel.org>
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, 10 May 2019, Sasha Levin wrote:

> 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.  We needed it for 4.19, I wasn't sure how far it would patch 
back so I left the version off.  BFQ was merged in 4.12 iirc, so if it 
patched against 4.14, then 4.19 and 4.14 are the only ones that need it.

--
Eric Wheeler


> 
> --
> Thanks,
> Sasha
>