Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758375Ab1BRVqK (ORCPT ); Fri, 18 Feb 2011 16:46:10 -0500 Received: from imr4.ericy.com ([198.24.6.8]:52490 "EHLO imr4.ericy.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757191Ab1BRVqI convert rfc822-to-8bit (ORCPT ); Fri, 18 Feb 2011 16:46:08 -0500 From: Dominique Toupin To: Steven Rostedt CC: Mathieu Desnoyers , Masami Hiramatsu , "linux-kernel@vger.kernel.org" , Ingo Molnar , Andrew Morton , Thomas Gleixner , Frederic Weisbecker , "H. Peter Anvin" , Andi Kleen , "2nddept-manager@sdl.hitachi.co.jp" <2nddept-manager@sdl.hitachi.co.jp> Date: Fri, 18 Feb 2011 16:45:31 -0500 Subject: RE: [RFC][PATCH 0/4] ftrace: Use -mfentry when supported (this is for x86_64 right now) Thread-Topic: [RFC][PATCH 0/4] ftrace: Use -mfentry when supported (this is for x86_64 right now) Thread-Index: AcvPq5P826IDTfQrQKuB8/vxoFUeuwABJMBg Message-ID: References: <20110209200249.111932716@goodmis.org> <4D5D1672.6070206@hitachi.com> <1297948703.23343.907.camel@gandalf.stny.rr.com> <4D5D4013.4070602@hitachi.com> <1297957591.23343.921.camel@gandalf.stny.rr.com> <4D5D47C0.9020206@hitachi.com> <1297973501.23343.953.camel@gandalf.stny.rr.com> <4D5E5BCF.1040509@hitachi.com> <1298041659.23343.956.camel@gandalf.stny.rr.com> <20110218151954.GA27834@Krystal> <1298061395.23343.975.camel@gandalf.stny.rr.com> In-Reply-To: <1298061395.23343.975.camel@gandalf.stny.rr.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2076 Lines: 48 If it's 1 us it might be OK for some of our "server" type of system, still the number of cores are growing quite fast and stopping _all_ of them is a bit scary. Some cores are dedicated to a special telecom subsystem which is very sensitive to even very small hic-up, we don't want to stop those cores. As background info, we can use GDB dynamic tracepoint in those systems because GDB doesn't stop all cores when the tracepoint are inserted with a jump. > -----Original Message----- > From: Steven Rostedt [mailto:rostedt@goodmis.org] > Sent: 18-Feb-11 15:37 > To: Dominique Toupin > Cc: Mathieu Desnoyers; Masami Hiramatsu; > linux-kernel@vger.kernel.org; Ingo Molnar; Andrew Morton; > Thomas Gleixner; Frederic Weisbecker; H. Peter Anvin; Andi > Kleen; 2nddept-manager@sdl.hitachi.co.jp > Subject: RE: [RFC][PATCH 0/4] ftrace: Use -mfentry when > supported (this is for x86_64 right now) > > On Fri, 2011-02-18 at 15:10 -0500, Dominique Toupin wrote: > > My understanding is stop_machine will stop all processors > for many ms. > > s/ms/us/ > > > > Even if most of our systems are not hard real-time they are > soft real-time and stopping all cores for a few ms is not allowed. > > We can stop a few threads while we are jump patching but > all processors is too much for us. > > I think I could hit a single ms if we enable full function > tracing which disables ~22,000 functions in one shot. But if > you enable full function tracing, the kernel can slow down > quite drastically, and that would even be more problematic > than a single ms hic-up. As hackbench showed a %150 slowdown > when function tracer was running. > > Now the last measurements I took was a few years ago and it > was on a 4 CPU box. Perhaps stop_machine() may be a bit more > expensive on a 1024 CPU box. > > -- 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/