linux-kernel - RE: RE: very low IOPS due to "block: reduce kblockd_mod_delayed_work

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Date:   Tue, 8 Feb 2022 18:34:19 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     'Oliver Sang' <oliver.sang@...el.com>,
        Jens Axboe <axboe@...nel.dk>,
        'Yin Fengwei' <fengwei.yin@...el.com>,
        "'linux-block@...r.kernel.org'" <linux-block@...r.kernel.org>
CC:     "'Alex Xu (Hello71)'" <alex_y_xu@...oo.ca>,
        "'ming.lei@...hat.com'" <ming.lei@...hat.com>,
        "'hch@....de'" <hch@....de>, Long Li <longli@...rosoft.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
        "'Li, Philip'" <philip.li@...el.com>,
        Rakesh Ginjupalli <Rakesh.Ginjupalli@...rosoft.com>
Subject: RE: RE: very low IOPS due to "block: reduce
 kblockd_mod_delayed_work_on() CPU consumption"

> From: Dexuan Cui
> Sent: Friday, January 21, 2022 10:15 PM
> To: Oliver Sang <oliver.sang@...el.com>; Jens Axboe <axboe@...nel.dk>; Yin
> Fengwei <fengwei.yin@...el.com>; linux-block@...r.kernel.org
> Cc: Alex Xu (Hello71) <alex_y_xu@...oo.ca>; ming.lei@...hat.com;
> hch@....de; Long Li <longli@...rosoft.com>; Michael Kelley (LINUX)
> <mikelley@...rosoft.com>; linux-kernel@...r.kernel.org; Li, Philip
> <philip.li@...el.com>; Rakesh Ginjupalli <Rakesh.Ginjupalli@...rosoft.com>
> Subject: RE: RE: very low IOPS due to "block: reduce
> kblockd_mod_delayed_work_on() CPU consumption"
> 
> > From: Oliver Sang <oliver.sang@...el.com>
> > Sent: Tuesday, December 28, 2021 5:49 AM
> >  ...
> > Hi Jens, Dexuan,
> >
> > On Tue, Dec 28, 2021 at 10:30:43AM +0800, Yin Fengwei wrote:
> > > Hi Jens, Dexuan,
> > >
> > > On 12/20/2021 1:15 PM, Dexuan Cui wrote:
> > > >> From: Jens Axboe <axboe@...nel.dk>
> > > >> Sent: Sunday, December 19, 2021 7:28 AM
> > > >>> ...
> > > >>> Dexuan, can you test this for your test case too? I'm going to queue
> > > >>> up a revert for -rc6 just in case.
> > > >>
> > > >> This one should be better...
> > > >> ...
> > > >> Jens Axboe
> > > >
> > > > Hi Jens, sorry -- unluckily I lost the test environment.. :-(
> > > > I pinged the user to set up the test environment again, but he's
> > > > on vacation till the beginning of January.
> > >
> > > We hit this issue in our testing env also and will help to verify
> > > your fixing patch. Thanks.
> >
> > as we reported in [1], we found cb2ac2912a cause big regressions in fxmark
> > tests.
> > "[block]  cb2ac2912a:
> > fxmark.ssd_f2fs_dbench_client_4_bufferedio.works/sec -66.0% regression"
> >
> > By applying the patch supplied by Jens Axboe in previous thread directly
> > upon cb2ac2912a, we confirmed the regression could be fixed:
> > ...
> > > Regards
> > > Yin, Fengwei
> 
> Hi Jens, Fengwei,
> I finally regained my test evnironment and tested Jens's Dec-19 patch
> (see https://www.spinics.net/lists/linux-block/msg78065.html) and it
> also worked fine for me, i.e. no excessive CPU utilization even with the
> default dm_mod.dm_mq_queue_depth=2048.
> 
> BTW, Jen's patch is not in the mainline yet. I tested it using the linux-block tree.
> 
> Thanks,
> -- Dexuan

Hi Jens, any plan to commit your 12/19/2021 patch? 
It works great according to Fengwei's and my test.