From: Jens Axboe <axboe@kernel.dk>
To: Paolo Valente <paolo.valente@linaro.org>
Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
ulf.hansson@linaro.org, linus.walleij@linaro.org,
broonie@kernel.org, bfq-iosched@googlegroups.com,
oleksandr@natalenko.name, hurikhan77+bko@gmail.com
Subject: Re: [PATCH BUGFIX RFC 0/2] reverting two commits causing freezes
Date: Fri, 18 Jan 2019 09:29:13 -0700 [thread overview]
Message-ID: <960acfd8-2425-2d30-41e9-4cd10bc20bdf@kernel.dk> (raw)
In-Reply-To: <c3b182a2-7f82-2860-436b-c1d59d6661ff@kernel.dk>
On 1/18/19 6:35 AM, Jens Axboe wrote:
> On 1/18/19 4:52 AM, Paolo Valente wrote:
>> Hi Jens,
>> a user reported a warning, followed by freezes, in case he increases
>> nr_requests to more than 64 [1]. After reproducing the issues, I
>> reverted the commit f0635b8a416e ("bfq: calculate shallow depths at
>> init time"), plus the related commit bd7d4ef6a4c9 ("bfq-iosched:
>> remove unused variable"). The problem went away.
>
> For reverts, please put the justification into the actual revert
> commit. With this series, if applied as-is, we'd have two patches
> in the tree that just says "revert X" without any hint as to why
> that was done.
>
>> Maybe the assumption in commit f0635b8a416e ("bfq: calculate shallow
>> depths at init time") does not hold true?
>
> It apparently doesn't! But let's try and figure this out instead of
> blindly reverting it. OK, I think I see it. For the sched_tags
> case, when we grow the requests, we allocate a new set. Hence any
> old cache would be stale at that point.
>
> How about something like this? It still keeps the code of having
> to update this out of the hot IO path, and only calls it when we
> actually change the depths.
>
> Totally untested...
Now tested, and it seems to work for me. Note that haven't tried to
reproduce the issue, I just verified that the patch functionally
does what it should - when depths are updated, the hook is invoked
and updates the internal BFQ depth map.
--
Jens Axboe
next prev parent reply other threads:[~2019-01-18 16:29 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-18 11:52 [PATCH BUGFIX RFC 0/2] reverting two commits causing freezes Paolo Valente
2019-01-18 11:52 ` [PATCH BUGFIX RFC 1/2] Revert "bfq-iosched: remove unused variable" Paolo Valente
2019-01-18 11:52 ` [PATCH BUGFIX RFC 2/2] Revert "bfq: calculate shallow depths at init time" Paolo Valente
2019-01-18 13:35 ` [PATCH BUGFIX RFC 0/2] reverting two commits causing freezes Jens Axboe
2019-01-18 16:29 ` Jens Axboe [this message]
2019-01-18 17:24 ` Paolo Valente
2019-01-18 17:36 ` Jens Axboe
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