From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756078AbZEFI2i (ORCPT ); Wed, 6 May 2009 04:28:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752259AbZEFI22 (ORCPT ); Wed, 6 May 2009 04:28:28 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:48948 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751619AbZEFI21 (ORCPT ); Wed, 6 May 2009 04:28:27 -0400 Date: Wed, 6 May 2009 10:28:14 +0200 From: Ingo Molnar To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Andrew Morton , Frederic Weisbecker Subject: Re: [PATCH 03/11] tracing: export stats of ring buffers to userspace Message-ID: <20090506082814.GB28675@elte.hu> References: <20090506042101.231470089@goodmis.org> <20090506042333.402933098@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090506042333.402933098@goodmis.org> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Steven Rostedt wrote: > From: Steven Rostedt > > This patch adds stats to the ftrace ring buffers: > > # cat /debugfs/tracing/per_cpu/cpu0/stats > entries: 42360 > overrun: 30509326 > commit overrun: 0 > nmi dropped: 0 > > Where entries are the total number of data entries in the buffer. > > overrun is the number of entries not consumed and were overwritten by > the writer. > > commit overrun is the number of entries dropped due to nested writers > wrapping the buffer before the initial writer finished the commit. > > nmi dropped is the number of entries dropped due to the ring buffer > lock being held when an nmi was going to write to the ring buffer. > Note, this field will be meaningless and will go away when the ring > buffer becomes lockless. > > [ Impact: let userspace know what is happening in the ring buffers ] nice! I was always wondering about these properties - Frederic reported that we drop a lot of trace entries when filtering is enabled, due to the rather stupid: reserve-buffer put-stuff-into-buffer drop-buffer-if-filter-false common sequence we do on heavily filtered input. Ingo