linux-kernel - Re: [LKP] Re: [xfs] bad77c375e: stress-ng.fallocate.ops_per

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Message-ID: <20211202220451.GT2206@rh>
Date:   Fri, 3 Dec 2021 09:04:51 +1100
From:   Dave Chinner <dchinner@...hat.com>
To:     Xing Zhengjun <zhengjun.xing@...ux.intel.com>
Cc:     kernel test robot <oliver.sang@...el.com>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Chandan Babu R <chandanrlinux@...il.com>,
        Brian Foster <bfoster@...hat.com>,
        Allison Henderson <allison.henderson@...cle.com>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        lkp@...el.com
Subject: Re: [LKP] Re: [xfs] bad77c375e: stress-ng.fallocate.ops_per_sec
 -10.0% regression

On Tue, Nov 30, 2021 at 02:46:06PM +0800, Xing Zhengjun wrote:
> Hi Dave,
> 
>    Do you have time to look at this? It still existed in v5.16-rc3. Thanks

AFAIC, it's a "don't care" issue.

The series of commits around this one:

> > > FYI, we noticed a -10.0% regression of
> > > stress-ng.fallocate.ops_per_sec due to commit:
> > > 
> > > 
> > > commit: bad77c375e8de6c776c848e443f7dc2d0d909be5 ("xfs: CIL
> > > checkpoint flushes caches unconditionally")
> > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master

changed how we manage FUA/cache flushes for the journal changed
performance across a wide range of workloads. Many went a lot
faster, some (like this one) went slightly slower. Overall it was a
net win, especially on storage stacks with really slow cache flushes
(e.g. dm-thinp) and workloads that do a lot of concurrent metadata
modification.

Overall, fallocate is not a performance critical path - it's a
slowpath because it serialises all IO to that file while the
fallocate call runs. Hence performance characteristics for fallocate
aren't really a major concern to begin with...

-Dave.
-- 
Dave Chinner
dchinner@...hat.com