From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266691AbUG0W5A (ORCPT ); Tue, 27 Jul 2004 18:57:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266689AbUG0W5A (ORCPT ); Tue, 27 Jul 2004 18:57:00 -0400 Received: from mustang.oldcity.dca.net ([216.158.38.3]:1706 "HELO mustang.oldcity.dca.net") by vger.kernel.org with SMTP id S266691AbUG0W4u (ORCPT ); Tue, 27 Jul 2004 18:56:50 -0400 Subject: Re: [patch] voluntary-preempt-2.6.8-rc2-L2, preemptable hardirqs From: Lee Revell To: Ingo Molnar Cc: linux-kernel , William Lee Irwin III , Lenar L?hmus , Andrew Morton , Arjan van de Ven In-Reply-To: <20040727162759.GA32548@elte.hu> References: <40F3F0A0.9080100@vision.ee> <20040713143947.GG21066@holomorphy.com> <1090732537.738.2.camel@mindpipe> <1090795742.719.4.camel@mindpipe> <20040726082330.GA22764@elte.hu> <1090830574.6936.96.camel@mindpipe> <20040726083537.GA24948@elte.hu> <1090832436.6936.105.camel@mindpipe> <20040726124059.GA14005@elte.hu> <20040726204720.GA26561@elte.hu> <20040727162759.GA32548@elte.hu> Content-Type: text/plain Message-Id: <1090969026.743.12.camel@mindpipe> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.6 Date: Tue, 27 Jul 2004 18:57:07 -0400 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2004-07-27 at 12:27, Ingo Molnar wrote: > i've uploaded -L2: > > http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.8-rc2-L2 > > the hardirq-redirection feature is activated via voluntary-preemption=3 > (default). All irqs except the timer irq are redirected. (the timer irq > needs to run from irq context - but it has constant latency and constant > frequency so it's not an issue. Soft timers are executed from the timer > softirq which is redirected and hence preemptable.) > > this means that with this patch applied the 2.6 UP kernel is quite close > to being hard-RT capable (using controlled drivers and workloads). All > unbound-latency asynchronous workloads have been unloaded into > synchronous, schedulable process contexts - so nothing can delay a > high-prio RT task. (assuming we caught all the latencies. Any remaining > latency can be fixed with the existing methods.) > > i've done a softirq lock-break in the atkbd and ps2mouse drivers - this > should fix the big latencies triggered by NumLock/CapsLock, reported by > Lee Revell. > The Caps Lock problem goes away with voluntary-preempt=2. It makes sense that 3 would be problematic, as for audio work you don't want the soundcard interrupt redirected. The obvious next feature to add would be to make certain IRQs non-schedulable, like you would for an RT system. For an audio system this would be just the soundcard interrupt (and timer as stated above). Then, while it still might not be hard-RT, it would blow away anything achievable on the other OS'es people do audio work with. Lee