Re: Real-Time Preemption, -RT-2.6.10-rc2-mm3-V0.7.31-7

[Ingo Molnar <mingo@elte.hu>]

* Rui Nuno Capela <rncbc@rncbc.org> wrote:

>     xruntrace1-2.6.10-rc2-mm3-RT-V0.7.31-13-*.trc.gz
>         - the captured traces, as dumped with xruntrace1_watch.sh script.

> Each trace shows only the first XRUN occurrence on a distinct jackd
> session. Every other trace were triggered and captured after
> restarting jackd.

interesting - the trace shows only a latency of 20-40 usecs. Perhaps the
tracing should be done over two periods?

Could you try to hack alsa_driver.c to do the gettimeofday(1,1) call for
only every second case. Something like this ought to be enough:

	{
		static count = 0;

		if (!(count++ & 1))
			gettimeofday(0,1);
	}

(only one thread accesses this particular variable so there are no
threading issues.)

with this variant there's a 50% chance that we get the trace of the last
2 poll() instances. (and there's a 50% chance that we get only 1 period
covered.)

in any case, the scripts & approach seems to be almost there, i hope we
only need the above change to see the true source of the xruns.

	Ingo