Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764492AbZDCOMf (ORCPT ); Fri, 3 Apr 2009 10:12:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753816AbZDCOMY (ORCPT ); Fri, 3 Apr 2009 10:12:24 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.123]:51140 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753807AbZDCOMX (ORCPT ); Fri, 3 Apr 2009 10:12:23 -0400 Date: Fri, 3 Apr 2009 10:12:18 -0400 (EDT) From: Steven Rostedt X-X-Sender: rostedt@gandalf.stny.rr.com To: Ingo Molnar cc: Tom Zanussi , "Paul E. McKenney" , linux-kernel , fweisbec@gmail.com Subject: Re: [PATCH] tracing/filters: allow event filters to be set only when not tracing In-Reply-To: <20090403135956.GD8875@elte.hu> Message-ID: References: <1238390546.6368.65.camel@bookworm> <20090401122408.GG12966@elte.hu> <1238653371.6655.48.camel@bookworm> <20090403135956.GD8875@elte.hu> 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: 2152 Lines: 54 On Fri, 3 Apr 2009, Ingo Molnar wrote: > > * Tom Zanussi wrote: > > > On Wed, 2009-04-01 at 14:24 +0200, Ingo Molnar wrote: > > > * Tom Zanussi wrote: > > > > > > > This patch adds code allowing the event filter to be set only if > > > > there's no active tracing going on. > > > > > > > --- a/kernel/trace/trace_events.c > > > > +++ b/kernel/trace/trace_events.c > > > > @@ -498,6 +498,9 @@ event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt, > > > > struct filter_pred *pred; > > > > int err; > > > > > > > > + if (tracing_is_enabled() && (!tracer_is_nop() || call->enabled)) > > > > + return -EBUSY; > > > > > > hm, but it would be the normal use-case to set filters on the fly. > > > To experiment around with them and shape them until the output is > > > just right. Having to turn the tracer on/off during that seems quite > > > counterproductive to that use-case. > > > > > > > I didn't see anything that could be used to temporarily disable > > tracing (tracing_stop() and tracing_start() are 'quick' versions > > that mostly just disable recording), so did it this way to avoid > > adding any overhead to the filter-checking code. > > > > But anyway, I'll post a new patch shortly that uses rcu and does > > allow the filters to be set on the fly. > > that's a very intelligent way to do it! > > There's a theoretical problem though: what if we put a filtered > tracepoint into the RCU code? Especially if that tracepoint is in > the common function-tracer callback affecting all kernel functions. > I've Cc:-ed Paul. I think the quiescent state logic should handle > this just fine, but i'm not 100% sure. I commented about this too. I feel the safest way is to simply use preempt_disable, and instead of synchronize_rcu, we can use synchronize_sched, which should have the same effect. -- 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/