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@suse.de> 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.