On 12-02-22 11:20 AM, Felix Kuehling wrote: > On 12-02-21 07:49 PM, Mario Kleiner wrote: >> On 02/21/2012 09:07 PM, Alex Deucher wrote: > [snip] >>> The fix looks ok to me. Mario any thoughts? >>> >>> Reviewed-by: Alex Deucher<alexdeucher at gmail.com> >>> >> Hi, >> >> the fix looks ok to me for that device, but could we make it >> conditional on the AMD C-50 APU and similar pieces? It is the right >> thing to do for that gpu, but for regular desktop gpus it is too >> pessimistic if it defers the pageflip timestamping and completion >> event for an already completed flip: >> >> 1. Makes the timestamps 1 refresh too late, causing timing sensitive >> software like mine to detect false positives -- reporting skipped >> frames were there weren't any. Not as bad as missing a really skipped >> frame, but still not great. > Agreed. I was going to perform some more experiments on other hardware > to determine what the right threshold is for different hardware > generations. I hope I'll get to that this week.
I have a final version of my patch including an explanation of the observations it's based on (attached). It's against current drm-next from git://people.freedesktop.org/~airlied/linux. > >> 2. Can reduce the framerate due to throttling the client, especially >> on systems that are already challenged wrt. to their irq timing. >> >> Is the vblank period very short on these kind of devices? From Felix >> description is sounds as if it is only 2 scanlines? > It looks like that. Turns out that that's not correct. Smaller negative values of vpos never showed up in my log output because I didn't print it in case update_pending was 0. The actual vblank period is 8 scan lines on this device. Still not much compared to the ~40 I was seeing with an external monitor. Anything > -4 would result in flickering in my experiments, so only 5 scan lines worth of time are available for submitting the page flip in time for the next frame. If I miss that time window, the flip is deferred by an extra frame. In practice that seems to occur in about 25% of cases on this particular device. Regards, Felix > Thanks for the feedback, > Felix > >> thanks, >> -mario >> -- _____ Felix Kuehling \ _ | MTS Software Development Eng. /|_| | SW-Linux Base Gfx | AMD |__/ \| T 905.882.2600 x8928
