On 6 July 2010 20:53, Philipp Überbacher <hollunder@xxxxxxxxxxx> wrote: > Excerpts from Pedro Ribeiro's message of 2010-07-06 13:19:31 +0200: >> Hi, >> >> I've been using -rt kernels since 2.6.29 because I do realtime audio >> on my laptop. >> >> The audio stability has been steadily improving since, and now I find >> that I can use 2.6.34 without the -rt patch and achieve the same >> stability as 2.6.33-rt - well, my latency requirements aren't that >> high, I just need to maintain 8.9ms completely stable, however before >> .34 it would be impossible without the -rt patch. >> >> So out of curiosity, what changed for .34? According to [1], on .33 >> Raw Spinlock Annotation was introduced in the mainline kernel. >> However, as said above, I can't get the same performance than with >> .34. >> >> I remember that I read somewhere that the one the biggest problems >> with latency requirements was the use of the BKL. Do you think there >> will be a significant improvement of latency (in specific cases of >> course) with the scheduled removal of BKL for 2.6.36? >> >> Thanks for the help, >> Pedro >> >> [1] http://www.osadl.org/Realtime-Linux.projects-realtime-linux.0.html > > Ah, nice to hear that the BKL removal is scheduled. Pretty much all I > know is that Linus set the BKL removal as precondition for preempt-rt to > be merged with mainline. > I guess this means that preempt-rt could disappear in some post-.36 > version. I won't hold my breath. > Anyway, the stock kernel has been good for a while, but there are some > cases where I still experience big differences. Some, mostly audio > unrelated, actions or kinds of load cause lots of xruns with the stock > kernel and none with -rt. Prime example for me is xrandr, enable an > external monitor -> xruns, not so with -rt. There are a couple of other > cases. It's mostly about this kind of stuff, the achievable latency is > pretty much the same in my experience (which is only with an USB > interface). > -- > Regards, > Philipp > > -- I agree with you that there are some corner cases where you can trigger xruns. However, I noticed a very big difference with 2.6.34. It was easy to trigger xruns, even with .33-rt in the following situations: - physical memory full, swap at 20% - change virtual desktop (yes strange but it always triggered it) - running cpu intensive apps - lots of disk i/o happening With vanilla .34, ALL of the above disappeared except the disk i/o thing. I can safely say that .34 is more stable than .33-rt with the latency I need (6 to 8 ms). I'm using USB audio snd-usb-caiaq, and barely anything changed between the two kernel versions. I still would not use it for live performance, but then again, I don't do them :) Regards, Pedro -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
