From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [Xenomai-help] Beginner's question / testsuite / latency From: Philippe Gerum In-Reply-To: <17613.60380.820599.627459@domain.hid> References: <442248c90607201417m24729b7cs23a8b82b719ff1cc@domain.hid> <200607221152.34298.bidsonux@domain.hid> <44C25DB0.50601@domain.hid> <200607282317.34990.bidsonux@domain.hid> <44CB6EB3.5070707@domain.hid> <1154282619.4970.25.camel@domain.hid> <44CD099F.9010507@domain.hid> <1154294584.4970.49.camel@domain.hid> <17613.60380.820599.627459@domain.hid> Content-Type: text/plain Date: Mon, 31 Jul 2006 16:19:24 +0200 Message-Id: <1154355564.5015.12.camel@domain.hid> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Reply-To: rpm@xenomai.org List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: xenomai@xenomai.org, Jan Kiszka 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. -- Philippe.