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

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Message-ID: <BYAPR21MB1270F7AC484CBDFD94B10726BF5C9@BYAPR21MB1270.namprd21.prod.outlook.com>
Date:   Sat, 22 Jan 2022 06:14:33 +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: 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