linux-kernel - Re: [PATCHSET v2 block/for-5.8] iocost: improve use

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Message-ID: <dd55f890-740c-16b5-77bd-4c6fdb710b3d@gmail.com>
Date:   Mon, 13 Apr 2020 19:56:26 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Tejun Heo <tj@...nel.org>, axboe@...nel.dk
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, cgroups@...r.kernel.org, newella@...com,
        josef@...icpanda.com, ming.lei@...hat.com, bvanassche@....org
Subject: Re: [PATCHSET v2 block/for-5.8] iocost: improve use_delay and latency
 target handling

On 13/04/2020 19:27, Tejun Heo wrote:
> Changes from v1[1]
> 
> * Dropped 0002-block-add-request-io_data_len.patch and updated to use
>   rq->stats_sectors instead as suggested by Pavel Begunkov.

rq->stats_sectors is set only when there is QUEUE_FLAG_STATS, see
blk_mq_start_request(). I don't see blk-iocost requiring it. Did I miss something?

> 
> This patchset improves the following two iocost control behaviors.
> 
> * iocost was failing to punish heavy shared IO generators (file metadata, memory
>   reclaim) through use_delay mechanism - use_delay automatically decays which
>   works well for iolatency but doesn't match how iocost behaves. This led to
>   e.g. memory bombs which generate a lot of swap IOs to use over their allotted
>   amount. This is fixed by adding non-decaying use_delay mechanism.
> 
> * The same latency targets were being applied regardless of the IO sizes. While
>   this works fine for loose targets, it gets in the way when trying to tigthen
>   them - a latency target adequate for a 4k IO is too short for a 1 meg IO.
>   iocost now discounts the size portion of cost when testing whether a given IO
>   met or missed its latency target.
> 
> While at it, it also makes minor changse to iocost_monitor.py.
> 
> This patchset contains the following five patches.
> 
>  0001-blk-iocost-switch-to-fixed-non-auto-decaying-use_del.patch
>  0002-blk-iocost-account-for-IO-size-when-testing-latencie.patch
>  0003-iocost_monitor-exit-successfully-if-interval-is-zero.patch
>  0004-iocost_monitor-drop-string-wrap-around-numbers-when-.patch
> 
> and is also available in the following git branch.
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git iocost-delay-latency-v2
> 
> diffstat follows. Thanks.
> 
>  block/Kconfig                  |    1 
>  block/blk-cgroup.c             |    6 ++++
>  block/blk-iocost.c             |   56 +++++++++++++++++++++++++++++------------
>  include/linux/blk-cgroup.h     |   43 ++++++++++++++++++++++++-------
>  tools/cgroup/iocost_monitor.py |   48 +++++++++++++++++++----------------
>  5 files changed, 106 insertions(+), 48 deletions(-)
> 
> --
> tejun
> 
> [1] http://lkml.kernel.org/r/20200408201450.3959560-1-tj@kernel.org
> 

-- 
Pavel Begunkov



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