linux-kernel - Re: [LKP] Re: [io_uring] 584b0180f0: phoronix-test-suite.fio.SequentialWrite.IO_uring.Yes.Yes.1MB.DefaultTestDirectory.mb

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Message-ID: <f5d20f6c-5363-231b-b208-b577a59b4ae9@kernel.dk>
Date:   Wed, 20 Jul 2022 11:24:14 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Yin Fengwei <fengwei.yin@...el.com>,
        kernel test robot <oliver.sang@...el.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, io-uring@...r.kernel.org,
        lkp@...ts.01.org, lkp@...el.com
Subject: Re: [LKP] Re: [io_uring] 584b0180f0:
 phoronix-test-suite.fio.SequentialWrite.IO_uring.Yes.Yes.1MB.DefaultTestDirectory.mb_s
 -10.2% regression

On 7/19/22 2:58 AM, Yin Fengwei wrote:
> Hi Jens,
> 
> On 7/19/2022 10:29 AM, Jens Axboe wrote:
>> I'll poke at this tomorrow.
> 
> Just FYI. Another finding (test is based on commit 584b0180f0):
> If the code block is put to different function, the fio performance result is
> different:

I think this turned out to be a little bit of a goose chase. What's
happening here is that later kernels defer the file assignment, which
means it isn't set if a request is queued with IOSQE_ASYNC. That in
turn, for writes, means that we don't hash it on io-wq insertion, and
then it doesn't get serialized with other writes to that file.

I'll come up with a patch for this that you can test.

-- 
Jens Axboe