Hi Ville,
On Sun, 2006-08-27 at 23:39 +0300, Ville Syrjälä wrote:
> 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.
Hmm, is there a way for me (not knowing what all this
SOFTRAP/PRIMPTR/fence stuff is all about) to test this? Is there some
place I can glean by what this interrupt is triggered and what it is
used for?
What would break if I patched mga_irq.c to not enable MGA_SOFTRAP?
Note that I'm observing the same behaviour on radeon, is it possible
that this driver has similar issues?
Thanks for your time,
Jan
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