Re: [PATCHSET v2 block/for-5.8] iocost: improve use_delay and latency target handling

From: Jens Axboe
Date: Thu Apr 30 2020 - 17:55:35 EST


On 4/13/20 10:27 AM, 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.
>
> 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(-)

Applied, thanks Tejun.

--
Jens Axboe