Hi Am 04.09.19 um 10:35 schrieb Feng Tang: > Hi Daniel, > > On Wed, Sep 04, 2019 at 10:11:11AM +0200, Daniel Vetter wrote: >> On Wed, Sep 4, 2019 at 8:53 AM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote: >>> >>> Hi >>> >>> Am 04.09.19 um 08:27 schrieb Feng Tang: >>>>> Thank you for testing. But don't get too excited, because the patch >>>>> simulates a bug that was present in the original mgag200 code. A >>>>> significant number of frames are simply skipped. That is apparently the >>>>> reason why it's faster. >>>> >>>> Thanks for the detailed info, so the original code skips time-consuming >>>> work inside atomic context on purpose. Is there any space to optmise it? >>>> If 2 scheduled update worker are handled at almost same time, can one be >>>> skipped? >>> >>> To my knowledge, there's only one instance of the worker. Re-scheduling >>> the worker before a previous instance started, will not create a second >>> instance. The worker's instance will complete all pending updates. So in >>> some way, skipping workers already happens. >> >> So I think that the most often fbcon update from atomic context is the >> blinking cursor. If you disable that one you should be back to the old >> performance level I think, since just writing to dmesg is from process >> context, so shouldn't change. > > Hmm, then for the old driver, it should also do the most update in > non-atomic context? > > One other thing is, I profiled that updating a 3MB shadow buffer needs > 20 ms, which transfer to 150 MB/s bandwidth. Could it be related with > the cache setting of DRM shadow buffer? say the orginal code use a > cachable buffer? > > >> >> https://unix.stackexchange.com/questions/3759/how-to-stop-cursor-from-blinking >> >> Bunch of tricks, but tbh I haven't tested them. > > Thomas has suggested to disable curson by > echo 0 > /sys/devices/virtual/graphics/fbcon/cursor_blink > > We tried that way, and no change for the performance data. There are several ways of disabling the cursor. On my test system, I entered tput civis before the test and got better performance. Did you try this as well? Best regards Thomas > > Thanks, > Feng > >> >> In any case, I still strongly advice you don't print anything to dmesg >> or fbcon while benchmarking, because dmesg/printf are anything but >> fast, especially if a gpu driver is involved. There's some efforts to >> make the dmesg/printk side less painful (untangling the console_lock >> from printk), but fundamentally printing to the gpu from the kernel >> through dmesg/fbcon won't be cheap. It's just not something we >> optimize beyond "make sure it works for emergencies". >> -Daniel >> >>> >>> Best regards >>> Thomas >>> >>>> >>>> Thanks, >>>> Feng >>>> >>>>> >>>>> Best regards >>>>> Thomas >>>> _______________________________________________ >>>> 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 >> >> >> >> -- >> Daniel Vetter >> Software Engineer, Intel Corporation >> +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- 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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