Hi I was traveling and could reply earlier. Sorry for taking so long. Am 13.08.19 um 11:36 schrieb Feng Tang: > Hi Thomas, > > On Mon, Aug 12, 2019 at 03:25:45PM +0800, Feng Tang wrote: >> 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. > > We also did some further break down for the time consumed by the > new code. > > The drm_fb_helper_dirty_work() calls sequentially > 1. drm_client_buffer_vmap (290 us) > 2. drm_fb_helper_dirty_blit_real (19240 us) > 3. helper->fb->funcs->dirty() ---> NULL for mgag200 driver > 4. drm_client_buffer_vunmap (215 us) > It's somewhat different to what I observed, but maybe I just couldn't reproduce the problem correctly. > The average run time is listed after the function names. > > From it, we can see drm_fb_helper_dirty_blit_real() takes too long > time (about 20ms for each run). I guess this is the root cause > of this regression, as the original code doesn't use this dirty worker. True, the original code uses a temporary buffer, but updates the display immediately. My guess is that this could be a caching problem. The worker runs on a different CPU, which doesn't have the shadow buffer in cache. > As said in last email, setting the prefer_shadow to 0 can avoid > the regrssion. Could it be an option? Unfortunately not. Without the shadow buffer, the console's display buffer permanently resides in video memory. It consumes significant amount of that memory (say 8 MiB out of 16 MiB). That doesn't leave enough room for anything else. The best option is to not print to the console. Best regards Thomas > Thanks, > Feng > >> >> --- 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 > _______________________________________________ > dri-devel mailing list > dri-devel@xxxxxxxxxxxxxxxxxxxxx > 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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