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Date: Mon, 23 Feb 2009 18:34:30 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
       Arnaldo Carvalho de Melo <acme@redhat.com>
Subject: Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites
Message-ID: <20090223173429.GJ5961@nowhere>
References: <49a1cc8f.2283420a.54d2.ffff8461@mx.google.com> <alpine.DEB.2.00.0902231034570.18221@gandalf.stny.rr.com> <alpine.DEB.2.00.0902231039290.18221@gandalf.stny.rr.com> <20090223162630.GG5961@nowhere> <alpine.DEB.2.00.0902231151020.18221@gandalf.stny.rr.com> <20090223170528.GH5961@nowhere> <alpine.DEB.2.00.0902231211230.18221@gandalf.stny.rr.com>
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On Mon, Feb 23, 2009 at 12:13:36PM -0500, Steven Rostedt wrote:
> 
> On Mon, 23 Feb 2009, Frederic Weisbecker wrote:
> 
> > On Mon, Feb 23, 2009 at 11:51:30AM -0500, Steven Rostedt wrote:
> > > 
> > > On Mon, 23 Feb 2009, Frederic Weisbecker wrote:
> > > > > 
> > > > > Perhaps we could add these callsites back, but we would need to update 
> > > > > trace_wake_up.
> > > > > 
> > > > > Have trace_wake_up set a flag instead, and add a tracepoint around the 
> > > > > scheduler (outside the grabbing of runqueue locks), that will have a 
> > > > > callback to the tracing code. That call back can perform the wakeups.
> > > > > 
> > > > > How does that sound?
> > > > 
> > > > 
> > > > That sounds good but only for these particular tracers I guess.
> > > 
> > > OK, what about making a trace_delay_wake_up()?
> > 
> > 
> > Which would send a delayed work to wake up?
> 
> No, I was thinking that trace_delay_wake_up() would be called by these 
> dangerous call sites. Then a per_cpu flag could be set. We could have a 
> trace point in the scheduler code that is outside holding a runqueue lock, 
> and this trace point would call a trace function that will clear the per 
> cpu flag, and then call trace_wake_up().
> 


Oh yes, sounds nice!

 
> -- Steve
>