From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755950AbZBYRe0 (ORCPT ); Wed, 25 Feb 2009 12:34:26 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753382AbZBYReR (ORCPT ); Wed, 25 Feb 2009 12:34:17 -0500 Received: from tomts13-srv.bellnexxia.net ([209.226.175.34]:40950 "EHLO tomts13-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752898AbZBYReR (ORCPT ); Wed, 25 Feb 2009 12:34:17 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Ap8EAK8KpUlMQWWY/2dsb2JhbACBbtdshBEG Date: Wed, 25 Feb 2009 12:34:12 -0500 From: Mathieu Desnoyers To: Jason Baron Cc: Masami Hiramatsu , KOSAKI Motohiro , Peter Zijlstra , "Frank Ch. Eigler" , mingo@elte.hu, rostedt@goodmis.org, linux-kernel@vger.kernel.org, acme@ghostprotocols.net, fweisbec@gmail.com Subject: Re: [PATCH] new irq tracer Message-ID: <20090225173412.GA14269@Krystal> References: <1234995035.4799.14.camel@laptop> <20090220195236.GB3104@redhat.com> <20090222123543.359C.A69D9226@jp.fujitsu.com> <49A5765C.2020001@redhat.com> <20090225165747.GC3123@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <20090225165747.GC3123@redhat.com> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 12:22:19 up 4 days, 8:56, 4 users, load average: 0.03, 0.24, 0.27 User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Jason Baron (jbaron@redhat.com) wrote: > On Wed, Feb 25, 2009 at 11:48:28AM -0500, Masami Hiramatsu wrote: > > KOSAKI Motohiro wrote: > > >> /** > > >> * handle_IRQ_event - irq action chain handler > > >> * @irq: the interrupt number > > >> @@ -354,7 +358,9 @@ irqreturn_t handle_IRQ_event(unsigned int irq, struct irqaction *action) > > >> local_irq_enable_in_hardirq(); > > >> > > >> do { > > >> + trace_irq_entry(irq); > > >> ret = action->handler(irq, action->dev_id); > > >> + trace_irq_exit(irq, ret); > > >> if (ret == IRQ_HANDLED) > > >> status |= action->flags; > > >> retval |= ret; > > > > > > Nobdy want unnecessary redundant tracepoint. > > > Please discuss with mathieu, and merge his tracepoint. > > > > Hmm, from the viewpoint of trouble shooting, the place of LTTng's tracepoint > > is enough. However, from the same viewpoint, it should pass irq-number > > to irq-exit event too, because we may lost some previous events by buffer-overflow > > etc. > > > > trace_irq_entry(irq, NULL); > > ret = _handle_IRQ_event(irq, action); > > trace_irq_exit(irq, ret); > > ^^^^ > > > > the lttng tracepoints wrap the calls to _handle_IRQ_event in 3 > different places. So the above suggested irq tracepoint provides the > same information with 4 less tracepoints in the code. So I believe its > simpler - plus we can understand which action handlers are handling the > interrupt. > The main thing I dislike about only tracing action->handler() calls is that you are not tracing an IRQ per se, but rather the invocation of a given handler within the interrupt. For instance, it would be difficult to calculate the maximum interrupt latency for a given interrupt line, because you don't have the "real" irq entry/exit events, just the individual handler() calls. But I agree that knowing which handler is called is important. How about this compromise : trace_irq_entry(irq, action) _handle_IRQ_event() for each action { trace_irq_handler(action, ret); ret = action->handler(irq, action->dev_id); ... } trace_irq_exit(action_ret); Would that give you the information you need ? Here trace_irq_handler would be passed the _current_ action invoked and the _previous_ action return value. Note that we should initialize irqreturn_t ret to some initial value if we do this. That should keep the tracing overhead minimal. Mathieu > thanks, > > -Jason > -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68