Message-ID: <60ae9ffa-88e0-1219-ee6a-269495055df2@suse.de>
Date:   Tue, 17 Sep 2019 10:48:14 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Rong Chen <rong.a.chen@...el.com>, michel@...nzer.net,
        linux-kernel@...r.kernel.org,
        dri-devel <dri-devel@...ts.freedesktop.org>, lkp@...org
Subject: Re: [LKP] [drm/mgag200] 90f479ae51: vm-scalability.median -18.8%
 regression

Hi

Am 16.09.19 um 11:06 schrieb Feng Tang:
> Hi Thomas,
> 
> On Mon, Sep 09, 2019 at 04:12:37PM +0200, Thomas Zimmermann wrote:
>> Hi
>>
>> Am 04.09.19 um 08:27 schrieb Feng Tang:
>>> Hi Thomas,
>>>
>>> On Wed, Aug 28, 2019 at 12:51:40PM +0200, Thomas Zimmermann wrote:
>>>> Hi
>>>>
>>>> Am 28.08.19 um 11:37 schrieb Rong Chen:
>>>>> Hi Thomas,
>>>>>
>>>>> On 8/28/19 1:16 AM, Thomas Zimmermann wrote:
>>>>>> Hi
>>>>>>
>>>>>> Am 27.08.19 um 14:33 schrieb Chen, Rong A:
>>>>>>> Both patches have little impact on the performance from our side.
>>>>>> Thanks for testing. Too bad they doesn't solve the issue.
>>>>>>
>>>>>> There's another patch attached. Could you please tests this as well?
>>>>>> Thanks a lot!
>>>>>>
>>>>>> The patch comes from Daniel Vetter after discussing the problem on IRC.
>>>>>> The idea of the patch is that the old mgag200 code might display much
>>>>>> less frames that the generic code, because mgag200 only prints from
>>>>>> non-atomic context. If we simulate this with the generic code, we should
>>>>>> see roughly the original performance.
>>>>>>
>>>>>>
>>>>>
>>>>> It's cool, the patch "usecansleep.patch" can fix the issue.
>>>>
>>>> Thank you for testing. But don't get too excited, because the patch
>>>> simulates a bug that was present in the original mgag200 code. A
>>>> significant number of frames are simply skipped. That is apparently the
>>>> reason why it's faster.
>>>
>>> Thanks for the detailed info, so the original code skips time-consuming
>>> work inside atomic context on purpose. Is there any space to optmise it?
>>> If 2 scheduled update worker are handled at almost same time, can one be
>>> skipped?
>>
>> We discussed ideas on IRC and decided that screen updates could be
>> synchronized with vblank intervals. This may give some rate limiting to
>> the output.
>>
>> If you like, you could try the patch set at [1]. It adds the respective
>> code to console and mgag200.
> 
> I just tried the 2 patches, no obvious change (comparing to the
> 18.8% regression), both in overall benchmark and micro-profiling.
> 
> 90f479ae51afa45e 04a0983095feaee022cdd65e3e4 
> ---------------- --------------------------- 
>      37236 ±  3%      +2.5%      38167 ±  3%  vm-scalability.median
>       0.15 ± 24%     -25.1%       0.11 ± 23%  vm-scalability.median_stddev
>       0.15 ± 23%     -25.1%       0.11 ± 22%  vm-scalability.stddev
>   12767318 ±  4%      +2.5%   13089177 ±  3%  vm-scalability.throughput

Thank you for testing. I wish we'd seen at least some improvement.

Best regards
Thomas

> Thanks,
> Feng
> 
>>
>> Best regards
>> Thomas
>>
>> [1]
>> https://lists.freedesktop.org/archives/dri-devel/2019-September/234850.html
>>
>>>
>>> Thanks,
>>> Feng
>>>
>>>>
>>>> Best regards
>>>> Thomas
>>
>> -- 
>> Thomas Zimmermann
>> Graphics Driver Developer
>> SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany
>> GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
>> HRB 21284 (AG Nürnberg)
>>
> 
> 
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG Nürnberg)



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