linux-kernel - Re: [xfs] 610125ab1e: fsmark.app

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Date:   Mon, 9 Sep 2019 15:32:36 +1000
From:   Dave Chinner <dchinner@...hat.com>
To:     kernel test robot <rong.a.chen@...el.com>
Cc:     "Darrick J. Wong" <darrick.wong@...cle.com>,
        Christoph Hellwig <hch@....de>,
        LKML <linux-kernel@...r.kernel.org>, linux-xfs@...r.kernel.org,
        lkp@...org
Subject: Re: [xfs] 610125ab1e: fsmark.app_overhead -71.2% improvement

On Mon, Sep 09, 2019 at 09:58:49AM +0800, kernel test robot wrote:
> Greeting,
> 
> FYI, we noticed a -71.2% improvement of fsmark.app_overhead due to commit:

A negative improvement? That's somewhat ambiguous...

> 0e822255f95db400 610125ab1e4b1b48dcffe74d9d8 
> ---------------- --------------------------- 
>          %stddev     %change         %stddev
>              \          |                \  
>  1.095e+08           -71.2%   31557568        fsmark.app_overhead
>       6157           +95.5%      12034        fsmark.files_per_sec

So, the files/s rate doubled, and the amount of time spent in
userspace by the fsmark app dropped by 70%.

>     167.31           -47.3%      88.25        fsmark.time.elapsed_time
>     167.31           -47.3%      88.25        fsmark.time.elapsed_time.max

Wall time went down by 50%.

>      91.00            -8.8%      83.00        fsmark.time.percent_of_cpu_this_job_got
>     148.15           -53.2%      69.38        fsmark.time.system_time

As did system CPU.

IOWs, this change has changed create performance by a factor of 4 -
the file create is 2x faster for half the CPU spent.

I don't think this is a negative improvement - it's a large positive
improvement.  I suspect that you need to change the metric
classifications for this workload...

Cheers,

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