Messages in this thread | | | Subject | Re: 2.6.24-rt1: timing problems (was [git pull] x86/hrtimer/acpi fixes) | From | Fernando Lopez-Lezcano <> | Date | Mon, 28 Jan 2008 16:47:07 -0800 |
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On Mon, 2008-01-28 at 10:26 -0800, Fernando Lopez-Lezcano wrote: > On Sun, 2008-01-27 at 05:46 +0100, Mike Galbraith wrote: > > On Sat, 2008-01-26 at 17:59 -0800, Fernando Lopez-Lezcano wrote: > > > > > Hi Ingo... back to testing. > > > History: > > > > > > 2.6.23.x + rt has not been very usable for audio applications. > > > 2.6.24-rt1: same so far. > > > > > > Why: Jack keeps printing "delayed..." messages and has xruns which means > > > that somehow the timing is delayed more than what jack would think > > > reasonable. As in the case with an old timing bug, the problem > > > dissapears when booting the kernel with idle=poll. Other users of Planet > > > CCRMA are able to replicate the behavior, which goes away with idle=poll > > > or booting the machine with only one core. As a workaround I have been > > > packaging 2.6.22.x but now I'm not able to use that as the old rt14 > > > patch, suitably tweaked results in a non working kernel. > > > > > > So it looks like, again, timing is getting skewed when the jack process > > > jumps between cpus and thus jack sees timing jumps that are just not > > > happenning. > > > > > > This is with a build based on 2.6.24 using as a base the latest Fedora > > > rawhide source package plus 2.6.24-rt1. > > > > Do you have a simple testcase? (one which doesn't entail installing > > ccrma and becoming an audiophile) > > No, I don't at this point. > I'll see if I can cook something simple today... (naively thinking that > some short C code could test for the clock being actually monotonic > across cpus).
Sorry, no luck so far in writing something simple that will fail. I tried testing for the results from repeated calls to clock_gettime (what jack uses for timing by default) to actually be monotonic, while a script uses taskset to force a cpu switch and of course got no errors.
2.6.24-rt1 with idle=poll works fine, without it I get multiple problems with the jack internal timing, or least that is what it seems to me from the symptoms.
-- Fernando
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