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

Xing Zhengjun
2020-03-25T05:50:13Z

ping...
The issue still exists in v5.6-rc7.

On 3/4/2020 4:15 PM, Xing Zhengjun wrote:
> 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