From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx186.postini.com [74.125.245.186]) by kanga.kvack.org (Postfix) with SMTP id 891096B004D for ; Wed, 18 Jan 2012 05:17:43 -0500 (EST) Received: from /spool/local by e38.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 18 Jan 2012 03:17:42 -0700 Received: from d03relay01.boulder.ibm.com (d03relay01.boulder.ibm.com [9.17.195.226]) by d03dlp03.boulder.ibm.com (Postfix) with ESMTP id 553DE19D8026 for ; Wed, 18 Jan 2012 03:16:57 -0700 (MST) Received: from d03av04.boulder.ibm.com (d03av04.boulder.ibm.com [9.17.195.170]) by d03relay01.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q0IAGw0c129458 for ; Wed, 18 Jan 2012 03:16:58 -0700 Received: from d03av04.boulder.ibm.com (loopback [127.0.0.1]) by d03av04.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q0IAGqRX015658 for ; Wed, 18 Jan 2012 03:16:54 -0700 Date: Wed, 18 Jan 2012 15:37:52 +0530 From: Srikar Dronamraju Subject: Re: [PATCH v9 3.2 7/9] tracing: uprobes trace_event interface Message-ID: <20120118100752.GF15447@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <20120110114821.17610.9188.sendpatchset@srdronam.in.ibm.com> <20120110114943.17610.28293.sendpatchset@srdronam.in.ibm.com> <20120116131137.GB5265@m.brq.redhat.com> <20120117092838.GB10397@elte.hu> <20120117102231.GB15447@linux.vnet.ibm.com> <20120117122133.GB4959@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20120117122133.GB4959@elte.hu> Sender: owner-linux-mm@kvack.org List-ID: To: Ingo Molnar Cc: Jiri Olsa , Arnaldo Carvalho de Melo , Peter Zijlstra , Linus Torvalds , Oleg Nesterov , Andrew Morton , LKML , Linux-mm , Andi Kleen , Christoph Hellwig , Steven Rostedt , Roland McGrath , Thomas Gleixner , Masami Hiramatsu , Arnaldo Carvalho de Melo , Anton Arapov , Ananth N Mavinakayanahalli , Jim Keniston , Stephen Rothwell > > Have you tried to use 'perf probe' to achieve any useful > instrumentation on a real app? > > I just tried out the 'glibc:free' usecase and it's barely > usable. > Thanks for trying. Yes, I have actually place probes on free and malloc while building a kernel and it has worked for me. > Firstly, the recording very frequently produces overruns: > > $ perf record -e probe_libc:free -aR sleep 1 > [ perf record: Woken up 169 times to write data ] > [ perf record: Captured and wrote 89.674 MB perf.data (~3917919 samples) ] > Warning:Processed 1349133 events and lost 1 chunks! > I have seen the "lost chunks" but thats not always and mostly when I have run perf record for a very long time. But I have seen this even with just kernel probes too. So I didnt debug that. > Using -m 4096 made it work better. > > Adding -g for call-graph profiling caused 'perf report' to lock > up: > > perf record -m 4096 -e probe_libc:free -agR sleep 1 > perf report > [ loops forever ] > This actually works for me. I had CONFIG_PREEMPT not set. So I set it and tried with and without Jiri's fix. It still worked for me. Can you pass me your config that shows this hang so that I can try and fix it. > I've sent a testcase to Arnaldo separately. Note that perf > report --stdio appears to work. There are no changes in perf report because of uprobes. So the data collected from uprobes could trigger the hang. I was speculating that not disabling preemption that Jiri pointed out could be causing this. So I tried with and without but couldnt reproduce. Can I request you to see if Jiri's patch helps? Today with -g option, on one machine I do see a $ sudo perf report perf: Floating point exception I will take a look at this too. Other machines dont seem to show this error. > Regular '-e cycles -g' works fine, so this is a uprobes specific > bug. > -- Thanks and Regards Srikar -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org