Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754090AbZDFX7B (ORCPT ); Mon, 6 Apr 2009 19:59:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751262AbZDFX6w (ORCPT ); Mon, 6 Apr 2009 19:58:52 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:44602 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751235AbZDFX6w (ORCPT ); Mon, 6 Apr 2009 19:58:52 -0400 Date: Mon, 6 Apr 2009 16:58:50 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: Frederic Weisbecker , Tom Zanussi , Ingo Molnar , linux-kernel Subject: Re: [PATCH] tracing/filters: allow event filters to be set only when not tracing Message-ID: <20090406235850.GA20273@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1238830355.22495.55.camel@bookworm> <1238916865.7989.212.camel@tropicana> <20090405171146.GK6893@linux.vnet.ibm.com> <20090406161527.GD6988@linux.vnet.ibm.com> <20090406194417.GA5936@nowhere> <20090406201524.GF6988@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090406201524.GF6988@linux.vnet.ibm.com> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3073 Lines: 62 On Mon, Apr 06, 2009 at 01:15:24PM -0700, Paul E. McKenney wrote: > On Mon, Apr 06, 2009 at 03:52:55PM -0400, Steven Rostedt wrote: > > > > On Mon, 6 Apr 2009, Frederic Weisbecker wrote: > > > > > > > > > > > > > So assuming we can't use rcu for this, it would be nice to have a way to > > > > > > > > 'pause' tracing so the current filter can be removed i.e. some version > > > > > > > > of stop_trace()/start_trace() that make sure nothing is still executing > > > > > > > > or can enter filter_match_preds() while the current call->preds is being > > > > > > > > destroyed. Seems like it would be straightforward to implement for the > > > > > > > > event tracer, since each event maps to a tracepoint that could be > > > > > > > > temporarily unregistered/reregistered, but maybe not so easy for the > > > > > > > > ftrace tracers... > > > > > > > > > > > > > > In principle, it would be possible to rework RCU so that instead of the > > > > > > > whole idle loop being a quiescent state, there is a single quiescent state > > > > > > > at one point in each idle loop. The reason that I have been avoiding this > > > > > > > is that there are a lot of idle loops out there, and it would be a bit > > > > > > > annoying to (1) find them all and update them and (2) keep track of all of > > > > > > > them to ensure that new ones cannot slip in without the quiescent state. > > > > > > > > > > > > > > But it could be done if the need is there. Simple enough change. > > > > > > > The following patch shows the general approach, assuming that CPUs > > > > > > > are never put to sleep without entering nohz mode. > > > > > > > > > > > > > > Thoughts? > > > > > > > > > > > > I think using synchronize_sched() should be good enough for what we need. > > > > > > > > > > Again, as long as either (1) you are OK with synchronize_sched() > > > > > ignoring preempt-disable sequences in the idle loop or (2) we rework RCU > > > > > to add something like an rcu_idle() call in each idle loop. > > > > > > > > 3) add "notrace" to the idle functions ;-) > > > > > > > > But perhaps the rcu_idle might be the best idea. > > > > > > > > > And tracing the idle time is also sometimes very useful :-) > > > > Agreed. I guess choice 2 is the best answer. > > Fair enough! > > Would one of you please check the placement of the rcu_idle() in the > patch? Patch reproduced below for convenience. Hmmm... Do the start_critical_timings() and stop_critical_timings() functions have anything to do with ftrace()? It does not look like I can just bury RCU-idle controls in these functions, given that they are also invoked around call_console_drivers(), but if all the idle loops are surrounded by stop_critical_timings() and start_critical_timings(), that would ease location of all the idle loops. ;-) Thanx, Paul -- 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/