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Date: Wed, 29 Nov 2006 20:51:44 +0100 From: Ingo Molnar <mingo@...e.hu> To: Fernando Lopez-Lezcano <nando@...ma.Stanford.EDU> Cc: "Linux-Kernel," <linux-kernel@...r.kernel.org> Subject: Re: 2.6.19-rc6-rt8: alsa xruns * Fernando Lopez-Lezcano <nando@...ma.Stanford.EDU> wrote: > > ok, i reproduced something similar on one of my boxes and it turned > > out to be a tracer bug. I've uploaded -rt10, could you try it? (The > > xruns will likely remain, but at least the tracer should be more > > usable now to find out the reason for the xruns.) > > I'm testing -rt10 right now (your binary rpm). Looks like the number > and length of the xruns went down, at least for now. All below 2mSec - > jack is running 128x2 @ 48000Hz. I'll let it run for a while and > report the traces (I have a script that collects all traces above > 60us, but not all xruns trigger a trace). ok. How do you gather the traces, are you using manual control of tracing via prctl(0,1) / prctl(0,0) - or the built-in wakeup tracing method? The wakeup tracing method will detect fundamental problems in -rt scheduling, but other types of delays can be better debugged via explicit tracing. [jackd used to have the gettimeofday(0,1)/(0,0) hack - this API hack has been replaced by prctl(0,1)/(0,0) to start/stop tracing] Take a look at linux/scripts/trace-it.c on how to set up manually triggered tracing. [if you do that then all you need to do is to start/stop the trace - the kernel will do a maximum search and will record the longest delay between start/stop calls.] Also, can you see the xruns/latencies with latencytest too? (That one might be easier to reproduce for me.) Also, my experience is that if there's a short succession of latencies after each other, then it's usually the first trace that makes most sense to analyze - the others might just be 'followup' or 'secondary' delays caused by the tracing/printing overhead of the first trace. So generally i concentrate on the first trace. But if the traces are reasonably apart then each of them makes sense - and sometimes one trace is more informative than another. Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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