Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758164Ab2FOWKT (ORCPT ); Fri, 15 Jun 2012 18:10:19 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:5161 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757954Ab2FOWKQ (ORCPT ); Fri, 15 Jun 2012 18:10:16 -0400 X-Authority-Analysis: v=2.0 cv=D8PF24tj c=1 sm=0 a=ZycB6UtQUfgMyuk2+PxD7w==:17 a=XQbtiDEiEegA:10 a=MgfmKKM-MiAA:10 a=5SG0PmZfjMsA:10 a=Q9fys5e9bTEA:10 a=meVymXHHAAAA:8 a=ayC55rCoAAAA:8 a=pvuyzcT5f7YbdC04ncIA:9 a=PUjeQqilurYA:10 a=ZycB6UtQUfgMyuk2+PxD7w==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.80.29 Message-ID: <1339798214.25903.17.camel@gandalf.stny.rr.com> Subject: RE: [PATCH 3/6] pstore: Add persistent function tracing From: Steven Rostedt To: "Luck, Tony" Cc: Anton Vorontsov , Greg Kroah-Hartman , Kees Cook , Colin Cross , Frederic Weisbecker , Ingo Molnar , Arnd Bergmann , John Stultz , Shuah Khan , "arve@android.com" , Rebecca Schultz Zavin , Jesper Juhl , Randy Dunlap , Stephen Boyd , Thomas Meyer , Andrew Morton , Marco Stornelli , WANG Cong , "linux-kernel@vger.kernel.org" , "devel@driverdev.osuosl.org" , "linaro-kernel@lists.linaro.org" , "patches@linaro.org" , "kernel-team@android.com" Date: Fri, 15 Jun 2012 18:10:14 -0400 In-Reply-To: <3908561D78D1C84285E8C5FCA982C28F1931FC85@ORSMSX104.amr.corp.intel.com> References: <20120615170659.GA4060@lizard> <1339780111-12075-3-git-send-email-anton.vorontsov@linaro.org> <3908561D78D1C84285E8C5FCA982C28F1931FC30@ORSMSX104.amr.corp.intel.com> <1339797308.25903.8.camel@gandalf.stny.rr.com> <3908561D78D1C84285E8C5FCA982C28F1931FC85@ORSMSX104.amr.corp.intel.com> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.2.2-1+b1 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: 1466 Lines: 34 On Fri, 2012-06-15 at 22:00 +0000, Luck, Tony wrote: > > With function tracing the impact to performance is tremendous. Just > > recording two long words is a 130% hit to performance. Now multiply that > > to recording strings. > > If pstore is writing to a flash based backend - then there will be many > milli-seconds of delay. I think the time taken to convert from binary to > ascii would be insignificant. milli-seconds for recording? This would cripple the kernel. On slow machines, incorporating lockdep into function tracing (and other debug options) causes the system to live lock. Tracing the timer interrupt took so long that by the time it finished, the next timer triggered again. Heck, today you can pretty much live lock most machines if you enabled the option 'func_stack_trace' while function tracing without filtering. You may be able to get your system back again, but it usually takes several seconds to acknowledge each key stroke (if you're lucky, but we all know *you* are ;-) If we are talking about milli-seconds to record. Then this is a no go, as it wont be worth adding. I'm thinking their buffering system is much faster than that today, as they have shown examples already. -- 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/