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

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 05.08.19 um 09:28 schrieb Rong Chen:
> Hi,
> 
> On 8/5/19 3:02 PM, Feng Tang wrote:
>> Hi Thomas,
>>
>> On Sun, Aug 04, 2019 at 08:39:19PM +0200, Thomas Zimmermann wrote:
>>> Hi
>>>
>>> I did some further analysis on this problem and found that the blinking
>>> cursor affects performance of the vm-scalability test case.
>>>
>>> I only have a 4-core machine, so scalability is not really testable. Yet
>>> I see the effects of running vm-scalibility against drm-tip, a revert of
>>> the mgag200 patch and the vmap fixes that I posted a few days ago.
>>>
>>> After reverting the mgag200 patch, running the test as described in the
>>> report
>>>
>>>    bin/lkp run job.yaml
>>>
>>> gives results like
>>>
>>>    2019-08-02 19:34:37  ./case-anon-cow-seq-hugetlb
>>>    2019-08-02 19:34:37  ./usemem --runtime 300 -n 4 --prealloc
>>> --prefault
>>>      -O -U 815395225
>>>    917319627 bytes / 756534 usecs = 1184110 KB/s
>>>    917319627 bytes / 764675 usecs = 1171504 KB/s
>>>    917319627 bytes / 766414 usecs = 1168846 KB/s
>>>    917319627 bytes / 777990 usecs = 1151454 KB/s
>>>
>>> Running the test against current drm-tip gives slightly worse results,
>>> such as.
>>>
>>>    2019-08-03 19:17:06  ./case-anon-cow-seq-hugetlb
>>>    2019-08-03 19:17:06  ./usemem --runtime 300 -n 4 --prealloc
>>> --prefault
>>>      -O -U 815394406
>>>    917318700 bytes / 871607 usecs = 1027778 KB/s
>>>    917318700 bytes / 894173 usecs = 1001840 KB/s
>>>    917318700 bytes / 919694 usecs = 974040 KB/s
>>>    917318700 bytes / 923341 usecs = 970193 KB/s
>>>
>>> The test puts out roughly one result per second. Strangely sending the
>>> output to /dev/null can make results significantly worse.
>>>
>>>    bin/lkp run job.yaml > /dev/null
>>>
>>>    2019-08-03 19:23:04  ./case-anon-cow-seq-hugetlb
>>>    2019-08-03 19:23:04  ./usemem --runtime 300 -n 4 --prealloc
>>> --prefault
>>>      -O -U 815394406
>>>    917318700 bytes / 1207358 usecs = 741966 KB/s
>>>    917318700 bytes / 1210456 usecs = 740067 KB/s
>>>    917318700 bytes / 1216572 usecs = 736346 KB/s
>>>    917318700 bytes / 1239152 usecs = 722929 KB/s
>>>
>>> I realized that there's still a blinking cursor on the screen, which I
>>> disabled with
>>>
>>>    tput civis
>>>
>>> or alternatively
>>>
>>>    echo 0 > /sys/devices/virtual/graphics/fbcon/cursor_blink
>>>
>>> Running the the test now gives the original or even better results,
>>> such as
>>>
>>>    bin/lkp run job.yaml > /dev/null
>>>
>>>    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.
> 
> I set "echo 0 > /sys/devices/virtual/graphics/fbcon/cursor_blink" for
> both commits,
> and the regression has no obvious change.

Ah, I see. Thank you for testing. There are two questions that come to
my mind: did you send the regular output to /dev/null? And what happens
if you disable the cursor with 'tput civis'?

If there is absolutely nothing changing on the screen, I don't see how
the regression could persist.

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
> 
> f1f8555dfb9a70a2  90f479ae51afa45efab97afdde testcase/testparams/testbox
> ----------------  -------------------------- ---------------------------
>          %stddev      change         %stddev
>              \          |                \
>      43394             -20%      34575 ±  3%
> vm-scalability/performance-300s-8T-anon-cow-seq-hugetlb/lkp-knm01
>      43393             -20%      34575        GEO-MEAN
> vm-scalability.median
> 
> Best Regards,
> Rong Chen
> 
>>
>> 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?
>>
>> 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)


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