Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755401Ab0BAPoT (ORCPT ); Mon, 1 Feb 2010 10:44:19 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.125]:63999 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755053Ab0BAPoS (ORCPT ); Mon, 1 Feb 2010 10:44:18 -0500 X-Authority-Analysis: v=1.0 c=1 a=db5xdBbprZYA:10 a=7U3hwN5JcxgA:10 a=meVymXHHAAAA:8 a=L0Yyq6P2Bu0c8ooMiKEA:9 a=NIq1NPsk-6RvwV0qevEA:7 a=8NtfxfjWIq-rO41h2sDvtv0eVUQA:4 a=0kPLrQdw3YYA:10 a=jeBq3FmKZ4MA:10 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.89.75 Subject: Re: [patch 2/3] scheduler: add full memory barriers upon task switch at runqueue lock/unlock From: Steven Rostedt Reply-To: rostedt@goodmis.org To: Nick Piggin Cc: Mathieu Desnoyers , Peter Zijlstra , Linus Torvalds , akpm@linux-foundation.org, Ingo Molnar , linux-kernel@vger.kernel.org, KOSAKI Motohiro , "Paul E. McKenney" , Nicholas Miell , laijs@cn.fujitsu.com, dipankar@in.ibm.com, josh@joshtriplett.org, dvhltc@us.ibm.com, niv@us.ibm.com, tglx@linutronix.de, Valdis.Kletnieks@vt.edu, dhowells@redhat.com In-Reply-To: <1265037815.29013.0.camel@gandalf.stny.rr.com> References: <20100131205254.407214951@polymtl.ca> <20100131210013.446503342@polymtl.ca> <20100201073341.GH9085@laptop> <1265017350.24455.122.camel@laptop> <20100201101142.GE12759@laptop> <1265020561.24455.142.camel@laptop> <20100201104901.GH12759@laptop> <20100201144759.GD10894@Krystal> <20100201145831.GB19520@laptop> <1265037815.29013.0.camel@gandalf.stny.rr.com> Content-Type: text/plain; charset="ISO-8859-15" Organization: Kihon Technologies Inc. Date: Mon, 01 Feb 2010 10:44:12 -0500 Message-ID: <1265039052.29013.28.camel@gandalf.stny.rr.com> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1817 Lines: 39 On Mon, 2010-02-01 at 10:23 -0500, Steven Rostedt wrote: > On Tue, 2010-02-02 at 01:58 +1100, Nick Piggin wrote: > > On Mon, Feb 01, 2010 at 09:47:59AM -0500, Mathieu Desnoyers wrote: > > > * Nick Piggin (npiggin@suse.de) wrote: > > > > Well I just mean that it's something for -rt to work out. Apps can > > > > still work if the call is unsupported completely. > > > > > > OK, so we seem to be settling for the spinlock-based sys_membarrier() > > > this time, which is much less intrusive in terms of scheduler > > > fast path modification, but adds more system overhead each time > > > sys_membarrier() is called. This trade-off makes sense to me, as we > > > expect the scheduler to execute _much_ more often than sys_membarrier(). > > > > > > When I get confirmation that's the route to follow from both of you, > > > I'll go back to the spinlock-based scheme for v9. > > > > I think locking or cacheline bouncing DoS is just something we can't > > realistically worry too much about in the standard kernel. No further > > than just generally good practice of good scalability, avoiding > > starvations and long lock hold times etc. > > > > So I would prefer the simpler version that doesn't add overhead to > > ctxsw, at least for the first implementation. > > Acked-by: Steven Rostedt I'm in agreement with Nick on this issue. Peter, I think you are being a bit paranoid here. But that's a good thing. Anyone working in the scheduler must be paranoid. That's what brings out issues that people normally do no think about. :-) -- Steve -- 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/