On Monday 31 July 2006 16:19, Philippe Gerum wrote: > On Mon, 2006-07-31 at 13:39 +0200, Gilles Chanteperdrix wrote: > > Philippe Gerum wrote: > > > > I rather think, also when looking at Julien's second trace, that we > > > > have some issue with X in user-space here, probably in combination > > > > with weird VIA hardware stalling IRQ delivery for a "few" > > > > microseconds. Let's see if the irqbench gives similar results. > > > > > > The problem is that I can reproduce X-related jittery (> 2 ms in a > > > row) on one of my test boxen when dragging windows over the screen, > > > without triggering the NMI watchdog set to 100 us (and guess what, the > > > chipset in question is from VIA). > > > > IMHO there are two reasons why the NMI watchdog may not trig: > > - its code is broken (we already have an unsolved bug that shows us that > > maybe it does not work as we believe) > > - the NMI watchdog only counts busy cycles, so maybe the CPU is not busy > > during these 2 ms, it is spinning, waiting for the GPU to finish the > > work using the rep; nop instruction in order to allow power > > saving. But with interrupts off. > > > > Maybe disabling hardware acceleration in your X server configuration > > would help ? > > Yes it does. Option "NoAccel" in the Screen section fixes the latency on > the test box. Still, reinitializing X while the latency test runs causes > the latter to hang, albeit LOC is still flowing properly and the box > keeps going normally. OTOH, switching from text mode to graphic mode > does not perturbate the test anymore.
Some good news from my side : I did the same on my EPIA box (added Option "NoAccel" in the Device section referring to the Trident video driver) and since then the latency test works like a charm. Zero overrun, and a stable max value (around 50 microseconds), even when I launch multiple heavy applications at the same time. Display performance has obviously taken a bit hit, but this is not my main concern for now. Thanks for the tip, there is no way I would have figured that one out by myself ;) (Jan, Gilles, thx for all of your good advice too !) It's time for me to play with Xenomai now. Regards, Julien Heyman _______________________________________________ Xenomai-help mailing list [email protected] https://mail.gna.org/listinfo/xenomai-help
