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Subject: Re: [PATCH BUGFIX/IMPROVEMENT V2 0/3] three bfq fixes restoring service guarantees with random sync writes in bg
From: Paolo Valente <paolo.valente@linaro.org>
In-Reply-To: <1504199166.666.11.camel@gmx.de>
Date: Thu, 31 Aug 2017 19:12:57 +0200
Cc: Mel Gorman <mgorman@techsingularity.net>, Jens Axboe <axboe@kernel.dk>,
        linux-block <linux-block@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>, broonie@kernel.org,
        lee.tibbert@gmail.com, oleksandr@natalenko.name
Message-Id: <970115C1-6336-458D-BBD5-3E5054C4553D@linaro.org>
References: <20170831064631.2223-1-paolo.valente@linaro.org> <20170831144257.oa5nm6vzihpam6kw@techsingularity.net> <1504199166.666.11.camel@gmx.de>
To: Mike Galbraith <efault@gmx.de>
Sender: linux-kernel-owner@vger.kernel.org
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> Il giorno 31 ago 2017, alle ore 19:06, Mike Galbraith <efault@gmx.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