linux-kernel - Re: CFQ idling kills I/O performance on ext4 with blkio cgroup controller

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Message-ID: <20190612130446.GD14578@quack2.suse.cz>
Date:   Wed, 12 Jun 2019 15:04:46 +0200
From:   Jan Kara <jack@...e.cz>
To:     "Srivatsa S. Bhat" <srivatsa@...il.mit.edu>
Cc:     Paolo Valente <paolo.valente@...aro.org>,
        linux-fsdevel@...r.kernel.org,
        linux-block <linux-block@...r.kernel.org>,
        linux-ext4@...r.kernel.org, cgroups@...r.kernel.org,
        kernel list <linux-kernel@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Jeff Moyer <jmoyer@...hat.com>, Theodore Ts'o <tytso@....edu>,
        amakhalov@...are.com, anishs@...are.com, srivatsab@...are.com,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: CFQ idling kills I/O performance on ext4 with blkio cgroup
 controller

On Tue 11-06-19 15:34:48, Srivatsa S. Bhat wrote:
> On 6/2/19 12:04 AM, Srivatsa S. Bhat wrote:
> > On 5/30/19 3:45 AM, Paolo Valente wrote:
> >>
> [...]
> >> At any rate, since you pointed out that you are interested in
> >> out-of-the-box performance, let me complete the context: in case
> >> low_latency is left set, one gets, in return for this 12% loss,
> >> a) at least 1000% higher responsiveness, e.g., 1000% lower start-up
> >> times of applications under load [1];
> >> b) 500-1000% higher throughput in multi-client server workloads, as I
> >> already pointed out [2].
> >>
> > 
> > I'm very happy that you could solve the problem without having to
> > compromise on any of the performance characteristics/features of BFQ!
> > 
> > 
> >> I'm going to prepare complete patches.  In addition, if ok for you,
> >> I'll report these results on the bug you created.  Then I guess we can
> >> close it.
> >>
> > 
> > Sounds great!
> >
> 
> Hi Paolo,
> 
> Hope you are doing great!
> 
> I was wondering if you got a chance to post these patches to LKML for
> review and inclusion... (No hurry, of course!)
> 
> Also, since your fixes address the performance issues in BFQ, do you
> have any thoughts on whether they can be adapted to CFQ as well, to
> benefit the older stable kernels that still support CFQ?

Since CFQ doesn't exist in current upstream kernel anymore, I seriously
doubt you'll be able to get any performance improvements for it in the
stable kernels...

								Honza

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR