Re: [LKP] Re: [ext4] b1b4705d54: filebench.sum_bytes_mb/s -20.2% regression

Xing Zhengjun
2020-03-04T08:15:44Z

Hi Matthew,

We test it in v5.6-rc4, the issue still exist, do you have time to
take a look at this? Thanks.

On 1/8/2020 10:31 AM, Rong Chen wrote:
>
>
> On 1/8/20 1:28 AM, Jan Kara wrote:
>> On Tue 07-01-20 11:57:08, Theodore Y. Ts'o wrote:
>>> On Tue, Jan 07, 2020 at 02:41:06PM +0100, Jan Kara wrote:
>>>> Hello,
>>>>
>>>> On Tue 24-12-19 08:59:15, kernel test robot wrote:
>>>>> FYI, we noticed a -20.2% regression of filebench.sum_bytes_mb/s due
>>>>> to commit:
>>>>>
>>>>>
>>>>> commit: b1b4705d54abedfd69dcdf42779c521aa1e0fbd3 ("ext4: introduce
>>>>> direct I/O read using iomap infrastructure")
>>>>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>>>>>
>>>>> in testcase: filebench
>>>>> on test machine: 8 threads Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz
>>>>> with 8G memory
>>>>> with following parameters:
>>>>>
>>>>>     disk: 1HDD
>>>>>     fs: ext4
>>>>>     test: fivestreamreaddirect.f
>>>>>     cpufreq_governor: performance
>>>>>     ucode: 0x27
>>>> I was trying to reproduce this but I failed with my test VM. I had
>>>> SATA SSD
>>>> as a backing store though so maybe that's what makes a difference.
>>>> Maybe
>>>> the new code results in somewhat more seeks because the five threads
>>>> which
>>>> compete in submitting sequential IO end up being more interleaved?
>>> A "-20.2% regression" should be read as a "20.2% performance
>>> improvement" is zero-day kernel speak.
>> Are you sure? I can see:
>>
>>       58.30 ±  2%     -20.2%      46.53        filebench.sum_bytes_mb/s
>>
>> which implies to me previously the throughput was 58 MB/s and after the
>> commit it was 46 MB/s?
>>
>> Anyway, in my testing that commit made no difference in that benchmark
>> whasoever (getting around 97 MB/s for each thread before and after the
>> commit).
>>                                 Honza
>
> We're sorry for the misunderstanding, "-20.2%" means the change of
> filebench.sum_bytes_mb/s,
> "regression" means the explanation of this change from LKP.
>
> Best Regards,
> Rong Chen
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--
Zhengjun Xing