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

[Rong Chen <rong.a.chen@intel.com>]

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Hi Thomas,

The previous throughput was reduced from 43955 to 35691, and there is a little increase in next-20200106,
but there is no obvious change after the patchset:
  
commit:
   f1f8555dfb ("drm/bochs: Use shadow buffer for bochs framebuffer console")
   90f479ae51 ("drm/mgag200: Replace struct mga_fbdev with generic framebuffer emulation")

f1f8555dfb9a70a2 90f479ae51afa45efab97afdde9
---------------- ---------------------------
          %stddev     %change         %stddev
              \          |                \
      43955 ±  2%     -18.8%      35691        vm-scalability.median

commit:

   9eb1b48ca4 ("Add linux-next specific files for 20200106")
   5f20199bac ("drm/fb-helper: Synchronize dirty worker with vblank")

  next-20200106  5f20199bac9b2de71fd2158b90
----------------  --------------------------
          %stddev      change         %stddev
              \          |                \
      38550                       38744
      38549                       38744        vm-scalability.median


Best Regards,
Rong Chen

On 1/6/20 9:19 PM, Thomas Zimmermann wrote:
> Hi Feng,
>
> do you still have the test setup that produced the performance penalty?
>
> If so, could you give a try to the patchset at [1]? I think I've fixed
> the remaining issues in earlier versions and I'd like to see if it
> actually improves performance.
>
> Best regards
> Thomas
>
> [1]
> https://lists.freedesktop.org/archives/dri-devel/2019-December/247771.html
>
> Am 05.08.19 um 14:52 schrieb Feng Tang:
>> Hi Thomas,
>>
>> On Mon, Aug 05, 2019 at 12:22:11PM +0200, Thomas Zimmermann wrote:
>>
>> 	[snip]
>>
>>>>>    2019-08-03 19:29:17  ./case-anon-cow-seq-hugetlb
>>>>>    2019-08-03 19:29:17  ./usemem --runtime 300 -n 4 --prealloc --prefault
>>>>>      -O -U 815394406
>>>>>    917318700 bytes / 659419 usecs = 1358497 KB/s
>>>>>    917318700 bytes / 659658 usecs = 1358005 KB/s
>>>>>    917318700 bytes / 659916 usecs = 1357474 KB/s
>>>>>    917318700 bytes / 660168 usecs = 1356956 KB/s
>>>>>
>>>>> Rong, Feng, could you confirm this by disabling the cursor or blinking?
>>>> Glad to know this method restored the drop. Rong is running the case.
>>>>
>>>> While I have another finds, as I noticed your patch changed the bpp from
>>>> 24 to 32, I had a patch to change it back to 24, and run the case in
>>>> the weekend, the -18% regrssion was reduced to about -5%. Could this
>>>> be related?
>>> In the original code, the fbdev console already ran with 32 bpp [1] and
>>> 16 bpp was selected for low-end devices. [2][3] The patch only set the
>>> same values for userspace; nothing changed for the console.
>> I did the experiment becasue I checked the commit
>>
>> 90f479ae51afa4 drm/mgag200: Replace struct mga_fbdev with generic framebuffer emulation
>>
>> in which there is code:
>>
>> diff --git a/drivers/gpu/drm/mgag200/mgag200_main.c b/drivers/gpu/drm/mgag200/mgag200_main.c
>> index b10f726..a977333 100644
>> --- a/drivers/gpu/drm/mgag200/mgag200_main.c
>> +++ b/drivers/gpu/drm/mgag200/mgag200_main.c
>> @@ -162,7 +162,7 @@ int mgag200_driver_load(struct drm_device *dev, unsigned long flags)
>>   	if (IS_G200_SE(mdev) && mdev->mc.vram_size < (2048*1024))
>>   		dev->mode_config.preferred_depth = 16;
>>   	else
>> -		dev->mode_config.preferred_depth = 24;
>> +		dev->mode_config.preferred_depth = 32;
>>   	dev->mode_config.prefer_shadow = 1;
>>   
>> My debug patch was kind of restoring of this part.
>>
>> Thanks,
>> Feng
>>
>>> Best regards
>>> Thomas
>>>
>>> [1]
>>> https://cgit.freedesktop.org/drm/drm-tip/tree/drivers/gpu/drm/mgag200/mgag200_fb.c?id=5d17718997367c435dbe5341a8e270d9b19478d3#n259
>>> [2]
>>> https://cgit.freedesktop.org/drm/drm-tip/tree/drivers/gpu/drm/mgag200/mgag200_fb.c?id=5d17718997367c435dbe5341a8e270d9b19478d3#n263
>>> [3]
>>> https://cgit.freedesktop.org/drm/drm-tip/tree/drivers/gpu/drm/mgag200/mgag200_fb.c?id=5d17718997367c435dbe5341a8e270d9b19478d3#n286
>>>
>>>> commit:
>>>>    f1f8555dfb9 drm/bochs: Use shadow buffer for bochs framebuffer console
>>>>    90f479ae51a drm/mgag200: Replace struct mga_fbdev with generic framebuffer emulation
>>>>    01e75fea0d5 mgag200: restore the depth back to 24
>>>>
>>>> f1f8555dfb9a70a2 90f479ae51afa45efab97afdde9 01e75fea0d5ff39d3e588c20ec5
>>>> ---------------- --------------------------- ---------------------------
>>>>       43921 ±  2%     -18.3%      35884            -4.8%      41826        vm-scalability.median
>>>>    14889337           -17.5%   12291029            -4.1%   14278574        vm-scalability.throughput
>>>>   
>>>> commit 01e75fea0d5ff39d3e588c20ec52e7a4e6588a74
>>>> Author: Feng Tang <feng.tang@intel.com>
>>>> Date:   Fri Aug 2 15:09:19 2019 +0800
>>>>
>>>>      mgag200: restore the depth back to 24
>>>>      
>>>>      Signed-off-by: Feng Tang <feng.tang@intel.com>
>>>>
>>>> diff --git a/drivers/gpu/drm/mgag200/mgag200_main.c b/drivers/gpu/drm/mgag200/mgag200_main.c
>>>> index a977333..ac8f6c9 100644
>>>> --- a/drivers/gpu/drm/mgag200/mgag200_main.c
>>>> +++ b/drivers/gpu/drm/mgag200/mgag200_main.c
>>>> @@ -162,7 +162,7 @@ int mgag200_driver_load(struct drm_device *dev, unsigned long flags)
>>>>   	if (IS_G200_SE(mdev) && mdev->mc.vram_size < (2048*1024))
>>>>   		dev->mode_config.preferred_depth = 16;
>>>>   	else
>>>> -		dev->mode_config.preferred_depth = 32;
>>>> +		dev->mode_config.preferred_depth = 24;>  	dev->mode_config.prefer_shadow = 1;
>>>>   
>>>>   	r = mgag200_modeset_init(mdev);
>>>>
>>>> Thanks,
>>>> Feng
>>>>
>>>>>
>>>>> The difference between mgag200's original fbdev support and generic
>>>>> fbdev emulation is generic fbdev's worker task that updates the VRAM
>>>>> buffer from the shadow buffer. mgag200 does this immediately, but relies
>>>>> on drm_can_sleep(), which is deprecated.
>>>>>
>>>>> I think that the worker task interferes with the test case, as the
>>>>> worker has been in fbdev emulation since forever and no performance
>>>>> regressions have been reported so far.
>>>>>
>>>>>
>>>>> So unless there's a report where this problem happens in a real-world
>>>>> use case, I'd like to keep code as it is. And apparently there's always
>>>>> the workaround of disabling the cursor blinking.
>>>>>
>>>>> 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@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>>


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