linux-kernel - Re: [lkp-robot] [xfs] b027d4c97b: fio.latency

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Date:   Wed, 6 Jun 2018 08:38:13 +1000
From:   Dave Chinner <david@...morbit.com>
To:     kernel test robot <xiaolong.ye@...el.com>
Cc:     Dave Chinner <dchinner@...hat.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Christoph Hellwig <hch@....de>,
        Carlos Maiolino <cmaiolino@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-xfs@...r.kernel.org,
        lkp@...org
Subject: Re: [lkp-robot] [xfs]  b027d4c97b:  fio.latency_2ms% +7.1% regression

On Tue, Jun 05, 2018 at 03:16:57PM +0800, kernel test robot wrote:
> 
> Greeting,
> 
> FYI, we noticed a +7.1%% regression of fio.latency_2ms% due to commit:
> 
> 
> commit: b027d4c97b9675c2ad75dec94be4e46dceb3ec74 ("xfs: don't retry xfs_buf_find on XBF_TRYLOCK failure")
> https://git.kernel.org/cgit/fs/xfs/xfs-linux.git xfs-4.18-merge
....
> 8925a3dc4771004b b027d4c97b9675c2ad75dec94b 
> ---------------- -------------------------- 
>          %stddev     %change         %stddev
>              \          |                \  
>      46.56 ±  3%      +7.1       53.61        fio.latency_2ms%
>       8.19            +0.2        8.40        fio.latency_100ms%
>       0.74 ±  3%      -0.1        0.68 ±  6%  fio.latency_250ms%
>      25.20 ±  6%      -7.3       17.86 ±  6%  fio.latency_4ms%
>       0.46 ±  9%      +0.2        0.69 ± 13%  fio.latency_750us%

This is not a regression. The number of IOs in the 4ms IO latency
bin has reduced by 7%, and inumber in the 2ms IO latency bin has
increased by 7%. IOWs, there's a measurable improvement in IO
latency as a result of those patches, not a regression.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com