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

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Date:   Wed, 28 Aug 2019 17:37:01 +0800
From:   Rong Chen <rong.a.chen@...el.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>,
        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 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.

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