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

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Message-Id: <DB3C26A6-11A4-4A5D-BCC5-20E03F7BFE59@linaro.org>
Date:   Thu, 31 Aug 2017 08:45:57 +0200
From:   Paolo Valente <paolo.valente@...aro.org>
To:     oleksandr@...alenko.name
Cc:     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,
        mgorman@...hsingularity.net, lee.tibbert@...il.com
Subject: Re: [PATCH BUGFIX/IMPROVEMENT 0/3] three bfq fixes restoring service guarantees with random sync writes in bg


> Il giorno 31 ago 2017, alle ore 08:41, oleksandr@...alenko.name ha scritto:
> 
>> Tested-by: Oleksander Natalenko <oleksandr@...alenko.name>
> 
> I'm "Oleksandr" :).
> 

Sorry, resending ...

Paolo

> 31.08.2017 08:10, Paolo Valente wrote:
>> 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.
>> The three patches in this series fix these bugs. These fixes restore
>> the usual BFQ service guarantees (and thus optimal responsiveness
>> too), against the above background workload and, probably, against
>> other similar workloads.
>> Thanks,
>> Paolo
>> [1] https://lkml.org/lkml/2017/8/9/957
>> Paolo Valente (3):
>>  block, bfq: make lookup_next_entity push up vtime on expirations
>>  block, bfq: remove direct switch to an entity in higher class
>>  block, bfq: guarantee update_next_in_service always returns an
>>    eligible entity
>> block/bfq-iosched.c |  4 +--
>> block/bfq-iosched.h |  4 +--
>> block/bfq-wf2q.c    | 91 ++++++++++++++++++++++++++++++++---------------------
>> 3 files changed, 60 insertions(+), 39 deletions(-)
>> --
>> 2.10.0