linux-kernel - Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

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Date:	Mon, 23 Feb 2009 19:09:41 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites


* Steven Rostedt <rostedt@...dmis.org> wrote:

> On Mon, 23 Feb 2009, Ingo Molnar wrote:
> 
> > * Steven Rostedt <rostedt@...dmis.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
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