On Sun, Aug 27, 2006 at 07:36:31PM +0200, Jan Gukelberger wrote:
> Hi,
>
> I'm trying to port an application that presents visual stimuli for
> experiments in neuroscience from DirectFBGL to X/DRI. A main requirement
> is reliable timing of the drawing code, i.e. on every VSYNC a new frame
> must be ready in the back buffer so that the buffers can be swapped.
>
> For this purpose I start a graphics thread with SCHED_FIFO scheduler
> that does basically this:
>
> while( !Stopped() )
> {
> glXGetVideoSyncSGI( &count1 );
> time1 = GetTime( CLOCK_REALTIME );
> glXWaitVideoSyncSGI( 2, ( count1 + 1 ) % 2, &count2 );
> time2 = GetTime( CLOCK_REALTIME );
> glXGetVideoSyncSGI( &count3 );
>
> if( count3 != prevCount + 1 )
> Print( "Lost %i frames.", count3 - prevCount - 1 );
> Print( "Draw time: %f ms. Wait time: %f ms.",
> time1 - prevTime, time2 - time1 );
> prevCount = count3;
> prevTime = time2;
>
> glFlush();
> glXSwapBuffers( dpy, win );
> DrawFrame();
> }
>
> Now my problem is: While all the drawing and buffer swapping and
> printing works "quite deterministic" [1] the glXWaitVideoSyncSGI call
> seems to "hang" from time to time, i.e. there are some occurrences where
> it takes between 20 and 50 ms to return instead of the normal say 15-16
> ms (@60Hz).
> The number of these "hangs" increases drastically from a few lost frames
> in 10000 frames when there's no load on the system to 1 lost in 5 frames
> when there's load on the X server, e.g. by 'tail -f'ing the log file in
> an xterm.
I think I saw this same issue on my G400 some time ago. It seems to be
caused by the SOFTRAP interrupt misbehaving. For some reason the
interrupt only works when there's some accelerator activity. My plan was
to see enabling status data writeback (PRIMPTR) would fix it, but I got
sidetracked and forgot the whole issue.
--
Ville Syrjälä
[EMAIL PROTECTED]
http://www.sci.fi/~syrjala/
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