From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754104AbZA2EoR (ORCPT ); Wed, 28 Jan 2009 23:44:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751688AbZA2En7 (ORCPT ); Wed, 28 Jan 2009 23:43:59 -0500 Received: from tomts13.bellnexxia.net ([209.226.175.34]:54992 "EHLO tomts13-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751375AbZA2En6 (ORCPT ); Wed, 28 Jan 2009 23:43:58 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AhIFAIjAgElMQWt2/2dsb2JhbACBbshohA+BOAY Date: Wed, 28 Jan 2009 23:43:56 -0500 From: Mathieu Desnoyers To: KOSAKI Motohiro Cc: ltt-dev@lists.casi.polymtl.ca, linux-kernel@vger.kernel.org Subject: Re: [ltt-dev] LTTng 0.87 improved page fault tracing Message-ID: <20090129044356.GA26018@Krystal> References: <20090127210203.GA13478@Krystal> <20090129123827.A959.KOSAKI.MOTOHIRO@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <20090129123827.A959.KOSAKI.MOTOHIRO@jp.fujitsu.com> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 23:36:36 up 28 days, 4:34, 2 users, load average: 0.06, 0.08, 0.02 User-Agent: Mutt/1.5.16 (2007-06-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * KOSAKI Motohiro (kosaki.motohiro@jp.fujitsu.com) wrote: > Hi > > interesting.. > > > I just combined the 4 page fault handler events that were in the tracing > > hot path of LTTng into 2 : > > > > kernel page_fault_entry > > kernel page_fault_exit > > > > They take as parameter the combination of what was available in the > > trap_entry/exit events and handle_mm_fault entry/exit events. This > > should lessen the performance impact of the tracer when it's active. > > I did the related modifications in LTTV 0.12.8. > > Just question. > > As far as I know, customer has two different requeremtn of the page fault. 1 a) > (1) collect number of all page fault > -> if it is too large, too many interrupt decrease performance. (a single event is required for this) 1 b) the user may also want to know the time spent in the page fault handler to service those faults, therefore involving page fault entry and exit events. > (2) collect number of major page fault > -> major page fault indicate to increase random access I/O, > then, some customer want to collect major page fault > (don't include minor page fault) Yes, the trace_page_fault_exit takes the "fault" parameter returned by handle_mm_fault (which is recorded to the trace as the "res" event field). Using res & VM_FAULT_MAJOR will give only the major page faults. Note that some knowledge of the bitmask is required to interpret the "res" bitfield. This could be done by a specific analysis module. I would ideally like to create a LTTng module to export tables including those bitfields so we can keep the bitfield interpretation in sync with the kernel code changes more or less automatically. > > Is this patch fill (2) requirement? > Yes. Mathieu > > -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68