Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932469Ab2EaUtb (ORCPT ); Thu, 31 May 2012 16:49:31 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:31922 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757975Ab2EaUt3 (ORCPT ); Thu, 31 May 2012 16:49:29 -0400 X-Authority-Analysis: v=2.0 cv=ae7jbGUt c=1 sm=0 a=ZycB6UtQUfgMyuk2+PxD7w==:17 a=XQbtiDEiEegA:10 a=nA43mK65oyIA:10 a=5SG0PmZfjMsA:10 a=Q9fys5e9bTEA:10 a=meVymXHHAAAA:8 a=ayC55rCoAAAA:8 a=5AuAxu6qg7pH1YH4f-gA:9 a=PUjeQqilurYA:10 a=ZycB6UtQUfgMyuk2+PxD7w==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.80.29 Message-ID: <1338497360.13348.438.camel@gandalf.stny.rr.com> Subject: Re: [PATCH 1/5] ftrace: Synchronize variable setting with breakpoints From: Steven Rostedt To: Peter Zijlstra Cc: Mathieu Desnoyers , linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Frederic Weisbecker , Masami Hiramatsu , "H. Peter Anvin" , Dave Jones , Andi Kleen , acme Date: Thu, 31 May 2012 16:49:20 -0400 In-Reply-To: <1338496857.28384.124.camel@twins> References: <20120531012829.160060586@goodmis.org> <20120531020440.476352979@goodmis.org> <1338462398.28384.52.camel@twins> <1338473302.13348.336.camel@gandalf.stny.rr.com> <1338486029.28384.93.camel@twins> <1338486820.13348.366.camel@gandalf.stny.rr.com> <1338487413.28384.103.camel@twins> <1338490218.13348.379.camel@gandalf.stny.rr.com> <1338491176.28384.114.camel@twins> <20120531195529.GA22976@Krystal> <1338495006.13348.418.camel@gandalf.stny.rr.com> <1338495969.28384.119.camel@twins> <1338496676.13348.430.camel@gandalf.stny.rr.com> <1338496857.28384.124.camel@twins> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.2.2-1 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1557 Lines: 57 On Thu, 2012-05-31 at 22:40 +0200, Peter Zijlstra wrote: > On Thu, 2012-05-31 at 16:37 -0400, Steven Rostedt wrote: > > On Thu, 2012-05-31 at 22:26 +0200, Peter Zijlstra wrote: > > > > > Right, but when you loose stop-machine you could simply do 30k > > > kmap_atomic/kunmap_atomic's consecutively since you're not holding > > > anybody up. > > > > It requires 3 IPIs per update too. Thus that's 90,000 IPIs you are > > blasting^Wsending to all CPUs. > > Uhm, no. > ----------------------------------+ > for_each() { | > kmap_atomic() | > frob int3 | > kunmap_atomic(); | > } | > | > sync-ipi-broadcast(); +--- Break points applied > | > for_each() { | > kmap_atomic(); | > frob tail | > kunmap_atomic(); | > } | ----------------------------------+ Note, for the above time, the entire kernel has breakpoints added, and every function is taking a hit due to it. By slowing down this process, the rest of the system *will* be impacted. Ideally, we want to finish it as quick as possible. Not to mention, the kmap_atomics will be slowed down by the breakpoints that are attached to them. -- Steve > > sync-ipi-broadcast(); > > for_each() { > kmap_atomic(); > frob head > kunmap_atomic(); > }; > > sync-ipi-broadcast(); > > How is that sending 90k ipis? -- 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/