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

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Message-ID: <alpine.DEB.2.00.0902231211230.18221@gandalf.stny.rr.com>
Date:	Mon, 23 Feb 2009 12:13:36 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>, 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


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().


-- Steve

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