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Date: Mon, 23 Feb 2009 19:09:41 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       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: <20090223180941.GA6015@elte.hu>
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* Steven Rostedt <rostedt@goodmis.org> wrote:

> On Mon, 23 Feb 2009, Ingo Molnar wrote:
> 
> > * Steven Rostedt <rostedt@goodmis.org> wrote:
> > 
> > > > 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().
> > 
> > No, that's very roundabout and ugly. If we putting a 
> > tracepoint there we might as well put real scheduler code 
> > there that looks for such a flag. But i'm not convinced we 
> > need a flag ...
> 
> Just a suggestion. I was trying to keep the tracer from being 
> an overhead. But what else would you suggest? Just having the 
> scheduler call trace_wakeup?

i think we could use a TIF flag to trigger a wakeup at the 
return-to-userspace (or return-from-IRQ) stage or so?

	Ingo