Hi Thomas,
On Fri, Aug 09, 2019 at 04:12:29PM +0800, Rong Chen wrote:
Hi,
Actually we run the benchmark as a background process, do we need to disable the cursor and test again?
There's a worker thread that updates the display from the shadow buffer. The blinking cursor periodically triggers the worker thread, but the actual update is just the size of one character.
The point of the test without output is to see if the regression comes from the buffer update (i.e., the memcpy from shadow buffer to VRAM), or from the worker thread. If the regression goes away after disabling the blinking cursor, then the worker thread is the problem. If it already goes away if there's simply no output from the test, the screen update is the problem. On my machine I have to disable the blinking cursor, so I think the worker causes the performance drop.
We disabled redirecting stdout/stderr to /dev/kmsg, and the regression is gone.
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 \ | \ 43785 44481 vm-scalability/300s-8T-anon-cow-seq-hugetlb/lkp-knm01 43785 44481 GEO-MEAN vm-scalability.median
Till now, from Rong's tests: 1. Disabling cursor blinking doesn't cure the regression. 2. Disabling printint test results to console can workaround the regression.
Also if we set the perfer_shadown to 0, the regression is also gone.
--- a/drivers/gpu/drm/mgag200/mgag200_main.c +++ b/drivers/gpu/drm/mgag200/mgag200_main.c @@ -167,7 +167,7 @@ int mgag200_driver_load(struct drm_device *dev, unsigned long flags) dev->mode_config.preferred_depth = 16; else dev->mode_config.preferred_depth = 32; - dev->mode_config.prefer_shadow = 1; + dev->mode_config.prefer_shadow = 0;
And from the perf data, one obvious difference is good case don't call drm_fb_helper_dirty_work(), while bad case calls.
Thanks, Feng
Best Regards, Rong Chen