Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756990AbZDFTxQ (ORCPT ); Mon, 6 Apr 2009 15:53:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752222AbZDFTw6 (ORCPT ); Mon, 6 Apr 2009 15:52:58 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.125]:38228 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753099AbZDFTw6 (ORCPT ); Mon, 6 Apr 2009 15:52:58 -0400 Date: Mon, 6 Apr 2009 15:52:55 -0400 (EDT) From: Steven Rostedt X-X-Sender: rostedt@gandalf.stny.rr.com To: Frederic Weisbecker cc: "Paul E. McKenney" , Tom Zanussi , Ingo Molnar , linux-kernel Subject: Re: [PATCH] tracing/filters: allow event filters to be set only when not tracing In-Reply-To: <20090406194417.GA5936@nowhere> Message-ID: References: <1238653371.6655.48.camel@bookworm> <20090403135956.GD8875@elte.hu> <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> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2227 Lines: 47 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. -- Steve -- 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/