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, broonie@kernel.org,
lee.tibbert@gmail.com, oleksandr@natalenko.name,
mirkomontanari91@gmail.com, angeloruocco90@gmail.com,
mauro.andreolini@unimore.it
Subject: Re: [PATCH BUGFIX/IMPROVEMENT 0/4] block, bfq: series of fixes of bugs affecting service guarantees
Date: Tue, 3 Oct 2017 08:41:10 -0600 [thread overview]
Message-ID: <f5649ee2-a807-6a9e-fb16-d9e14c40ab6f@kernel.dk> (raw)
In-Reply-To: <20170921090403.3217-1-paolo.valente@linaro.org>
On 09/21/2017 03:03 AM, Paolo Valente wrote:
> Hi,
> the first patch in this series fixes a bug that causes bfq to fail to
> guarantee a high responsiveness on some drives, if there is heavy
> random read+write I/O in the background. More precisely, such a
> failure allowed this bug to be found [1], but the bug may well cause
> other yet unreported anomalies.
>
> This fix uncovered other bugs that were concealed by the fixed bug,
> for rather subtle reasons. These further bugs caused similar
> responsiveness failures, but with sequential reaad+write workloads in
> the background. The remaining three patches fix these further bugs.
>
> The sum of these fixes makes responsiveness much stabler with BFQ. In
> the presence of write hogs, it is however still impossible for an I/O
> scheduler to guarantee perfect responsiveness in any circustance,
> because of throttling issues in the virtual-memory management
> subsystem, and in other higher-level components.
Added for 4.15, thanks.
--
Jens Axboe
prev parent reply other threads:[~2017-10-03 14:41 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-21 9:03 Paolo Valente
2017-09-21 9:04 ` [PATCH BUGFIX/IMPROVEMENT 1/4] block, bfq: fix wrong init of saved start time for weight raising Paolo Valente
2017-09-21 9:04 ` [PATCH BUGFIX/IMPROVEMENT 2/4] block, bfq: check and switch back to interactive wr also on queue split Paolo Valente
2017-09-21 9:04 ` [PATCH BUGFIX/IMPROVEMENT 3/4] block, bfq: let early-merged queues be weight-raised on split too Paolo Valente
2017-09-21 9:04 ` [PATCH BUGFIX/IMPROVEMENT 4/4] block, bfq: decrease burst size when queues in burst exit Paolo Valente
2017-10-03 14:41 ` Jens Axboe [this message]
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