From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?utf-8?q?Philipp_=C3=9Cberbacher?= Subject: Re: future of -rt kernels for realtime audio Date: Tue, 06 Jul 2010 21:53:37 +0200 Message-ID: <1278444945-sup-9886@eris> References: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE To: linux-rt-users Return-path: Received: from karen.lavabit.com ([72.249.41.33]:47450 "EHLO karen.lavabit.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754628Ab0GFTxq (ORCPT ); Tue, 6 Jul 2010 15:53:46 -0400 Received: from b.earth.lavabit.com (b.earth.lavabit.com [192.168.111.11]) by karen.lavabit.com (Postfix) with ESMTP id 302FC157557 for ; Tue, 6 Jul 2010 14:53:44 -0500 (CDT) Received: from localhost (eris.mozart.uni-klu.ac.at [143.205.216.185]) by lavabit.com with ESMTP id 9HSAS4NMC522 for ; Tue, 06 Jul 2010 14:53:40 -0500 In-reply-to: Sender: linux-rt-users-owner@vger.kernel.org List-ID: Excerpts from Pedro Ribeiro's message of 2010-07-06 13:19:31 +0200: > Hi, >=20 > I've been using -rt kernels since 2.6.29 because I do realtime audio > on my laptop. >=20 > 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. >=20 > 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. >=20 > 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? >=20 > Thanks for the help, > Pedro >=20 > [1] http://www.osadl.org/Realtime-Linux.projects-realtime-linux.0.htm= l 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 t= o 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). --=20 Regards, Philipp -- "Wir stehen selbst entt=C3=A4uscht und sehn betroffen / Den Vorhang zu = und alle Fragen offen." Bertolt Brecht, Der gute Mensch von Sezuan -- To unsubscribe from this list: send the line "unsubscribe linux-rt-user= s" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html