Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756860Ab0LJTgz (ORCPT ); Fri, 10 Dec 2010 14:36:55 -0500 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:48349 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755486Ab0LJTgy (ORCPT ); Fri, 10 Dec 2010 14:36:54 -0500 Date: Fri, 10 Dec 2010 19:17:20 +0000 From: Russell King - ARM Linux To: Peter Zijlstra Cc: Venkatesh Pallipadi , Mikael Pettersson , Ingo Molnar , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, John Stultz Subject: Re: [BUG] 2.6.37-rc3 massive interactivity regression on ARM Message-ID: <20101210191720.GC28263@n2100.arm.linux.org.uk> References: <1291920939.6803.38.camel@twins> <1291936593.13513.3.camel@laptop> <1291975704.6803.59.camel@twins> <1291987065.6803.151.camel@twins> <1291987635.6803.161.camel@twins> <1291988866.6803.171.camel@twins> <20101210175645.GB28263@n2100.arm.linux.org.uk> <1292004654.13513.38.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1292004654.13513.38.camel@laptop> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1579 Lines: 40 On Fri, Dec 10, 2010 at 07:10:54PM +0100, Peter Zijlstra wrote: > On Fri, 2010-12-10 at 17:56 +0000, Russell King - ARM Linux wrote: > > On Fri, Dec 10, 2010 at 02:47:46PM +0100, Peter Zijlstra wrote: > > > inline void update_rq_clock(struct rq *rq) > > > { > > > - int cpu = cpu_of(rq); > > > - u64 irq_time; > > > + s64 delta; > > > > > > if (rq->skip_clock_update) > > > return; > > > > > > - rq->clock = sched_clock_cpu(cpu); > > > - irq_time = irq_time_cpu(cpu); > > > - if (rq->clock - irq_time > rq->clock_task) > > > - rq->clock_task = rq->clock - irq_time; > > > + delta = sched_clock_cpu(cpu_of(rq)) - rq->clock; > > > + rq->clock += delta; > > > > Hmm. Can you tell me how this is different to: > > > > new_clock = sched_clock_cpu(cpu_of(rq)); > > delta = new_clock - rq->clock; > > rq->clock = new_clock; > > > > which I think may be simpler in terms of 64-bit math for 32-bit compilers > > to deal with? > > Its not, I could write it like that, the only reason I didn't is because > it uses an extra variable. If gcc on 32bit targets really generates > hideous code for it I'll happily change it. Well, I can't tell you what kind of code this produces on ARM, as it doesn't appear to apply to any kernel I've tried. So, I assume it's against some scheduler development tree rather than Linus' tree? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/