linux-kernel - Re: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3)

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Message-ID: <alpine.DEB.1.10.0808182359290.13401@gandalf.stny.rr.com>
Date:	Tue, 19 Aug 2008 00:00:17 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Scott Wood <scottwood@...escale.com>,
	Eran Liberty <liberty@...ricom.com>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	Steven Rostedt <srostedt@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3)


On Mon, 18 Aug 2008, Mathieu Desnoyers wrote:
> > > > 
> > > 
> > > Argh. See text_poke(). It's there exactly for this purpose on x86.
> > 
> > Ouch, I just did. text_poke is quite heavy. It would be interesting to see 
> > that performed on 20,000 locations at one time. I could play with it, but 
> > I'm a bit nervous.
> > 
> 
> It's alread used to modify the LOCK prefixes in alternative.c and did
> not seem to be too slow for that.. it should therefore be ok.

There's a lot more functions than locks ;-)

Anyway, this is only needed after system boot up. But then we do it ever 
time we start or stop tracing. I'll try it out and see if it is noticable.

-- Steve

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