linux-kernel - Re: [PATCH BUGFIX/IMPROVEMENT V2 0/3] three bfq fixes restoring service guarantees with random sync writes in bg

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Date:   Thu, 31 Aug 2017 19:12:57 +0200
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Mike Galbraith <efault@....de>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>, broonie@...nel.org,
        lee.tibbert@...il.com, oleksandr@...alenko.name
Subject: Re: [PATCH BUGFIX/IMPROVEMENT V2 0/3] three bfq fixes restoring service guarantees with random sync writes in bg


> Il giorno 31 ago 2017, alle ore 19:06, Mike Galbraith <efault@....de> ha scritto:
> 
> On Thu, 2017-08-31 at 15:42 +0100, Mel Gorman wrote:
>> On Thu, Aug 31, 2017 at 08:46:28AM +0200, Paolo Valente wrote:
>>> [SECOND TAKE, with just the name of one of the tester fixed]
>>> 
>>> Hi,
>>> while testing the read-write unfairness issues reported by Mel, I
>>> found BFQ failing to guarantee good responsiveness against heavy
>>> random sync writes in the background, i.e., multiple writers doing
>>> random writes and systematic fdatasync [1]. The failure was caused by
>>> three related bugs, because of which BFQ failed to guarantee to
>>> high-weight processes the expected fraction of the throughput.
>>> 
>> 
>> Queued on top of Ming's most recent series even though that's still a work
>> in progress. I should know in a few days how things stand.
> 
> It seems to have cured an interactivity issue I regularly meet during
> kbuild final link/depmod phase of fat kernel kbuild, especially bad
> with evolution mail usage during that on spinning rust.  Can't really
> say for sure given this is not based on measurement.
> 


Great!  Actually, when I found these bugs, I thought also about the
issues you told me you experienced with updatedb running.  But then I
forgot to tell you that these fixes might help.

Thanks,
Paolo

> 	-Mike