Hi Thomas, On Thu, Aug 22, 2019 at 07:25:11PM +0200, Thomas Zimmermann wrote: > Hi > > I was traveling and could reply earlier. Sorry for taking so long. No problem! I guessed so :) > > 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. Yes, that's my thought too. I profiled the working set size, for most of the drm_fb_helper_dirty_blit_real(), it will update a buffer 4096x768(3 MB), and as it is called 30~40 times per second, it surely will affect the 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. Do we have other options here? My thought is this is clearly a regression, that the old driver works fine, while the new version in linux-next doesn't. Also for a frame buffer console, writting dozens line of message to it is not a rare user case. We have many test platforms (servers/desktops/laptops) with different kinds of GFX hardwares, and this model works fine for many years :) Thanks, Feng > 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) > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
