linux-kernel - Re: [LKP] [drm/mgag200] 90f479ae51: vm-scalability.median -18.8% regression

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Date:   Wed, 28 Aug 2019 12:51:40 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Rong Chen <rong.a.chen@...el.com>, Feng Tang <feng.tang@...el.com>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>, michel@...nzer.net,
        lkp@...org, linux-kernel@...r.kernel.org,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [LKP] [drm/mgag200] 90f479ae51: vm-scalability.median -18.8%
 regression

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.

Best regards
Thomas

> commit:
>   f1f8555dfb9 drm/bochs: Use shadow buffer for bochs framebuffer console
>   90f479ae51a drm/mgag200: Replace struct mga_fbdev with generic
> framebuffer emulation
>   b976b04c2bc only schedule worker from non-atomic context
> 
> f1f8555dfb9a70a2  90f479ae51afa45efab97afdde b976b04c2bcf33148d6c7bc1a2 
> testcase/testparams/testbox
> ----------------  -------------------------- -------------------------- 
> ---------------------------
>          %stddev      change         %stddev      change %stddev
>              \          |                \          | \
>      42912             -15%      36517 44093
> vm-scalability/performance-300s-8T-anon-cow-seq-hugetlb/lkp-knm01
>      42912             -15%      36517 44093        GEO-MEAN
> vm-scalability.median
> 
> Best Regards,
> Rong Chen
> _______________________________________________
> 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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