linux-kernel - Re: [LKP] [btrfs] 8d47a0d8f7: fio.write_bw

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Date:   Fri, 10 Apr 2020 12:14:06 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Qu Wenruo <wqu@...e.com>
Cc:     Xing Zhengjun <zhengjun.xing@...ux.intel.com>,
        kernel test robot <rong.a.chen@...el.com>,
        David Sterba <dsterba@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Leonard Lausen <leonard@...sen.nl>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...org
Subject: Re: [LKP] [btrfs] 8d47a0d8f7: fio.write_bw_MBps -28.6% regression

On Fri, Apr 10, 2020 at 02:44:55PM +0800, Qu Wenruo wrote:
> On 2020/4/10 下午2:34, Xing Zhengjun wrote:
> > Hi Wenruo,
> > 
> >    We test it in v5.6, the issue still exist, do you have time to take a
> > look at this? Thanks.
> 
> This is expected.
> 
> The extra check brings new overhead mostly equal to another CRC32 run.
> 
> We believe it's worthy, as our read time tree checker has exposed quite
> some bit flip corruption.

The test probably runs on a PMEM device so there's no slowdown from the
actual IO and the in-memory checks are measurable, though 28% is a lot,
I'd expect something like 5-10% at most.