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: <8b2ad38d79334a156f18904cc2dd3509@natalenko.name>
Date:   Thu, 31 Aug 2017 08:41:18 +0200
From:   oleksandr@...alenko.name
To:     Paolo Valente <paolo.valente@...aro.org>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, 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

> Tested-by: Oleksander Natalenko <oleksandr@...alenko.name>

I'm "Oleksandr" :).

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