linux-kernel - Re: [PATCH BUGFIX/IMPROVEMENT 0/4] block, bfq: series of fixes of bugs affecting service guarantees

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Message-ID: <f5649ee2-a807-6a9e-fb16-d9e14c40ab6f@kernel.dk>
Date:   Tue, 3 Oct 2017 08:41:10 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Paolo Valente <paolo.valente@...aro.org>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        ulf.hansson@...aro.org, broonie@...nel.org, lee.tibbert@...il.com,
        oleksandr@...alenko.name, mirkomontanari91@...il.com,
        angeloruocco90@...il.com, mauro.andreolini@...more.it
Subject: Re: [PATCH BUGFIX/IMPROVEMENT 0/4] block, bfq: series of fixes of
 bugs affecting service guarantees

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