linux-kernel - Re: [PATCH/RFC 1/2] jump label: make enable/disable o(1)

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Message-ID: <1292530156.22905.1.camel@gandalf.stny.rr.com>
Date:	Thu, 16 Dec 2010 15:09:16 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jason Baron <jbaron@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, athieu.desnoyers@...ymtl.ca,
	hpa@...or.com, mingo@...e.hu, tglx@...utronix.de,
	andi@...stfloor.org, roland@...hat.com, rth@...hat.com,
	masami.hiramatsu.pt@...achi.com, fweisbec@...il.com,
	avi@...hat.com, davem@...emloft.net, sam@...nborg.org,
	ddaney@...iumnetworks.com, michael@...erman.id.au,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC 1/2] jump label: make enable/disable o(1)

On Thu, 2010-12-16 at 14:48 -0500, Jason Baron wrote:
>  
> > static inline int atomic_read(const atomic_t *v)
> > {
> >         return (*(volatile int *)&(v)->counter);
> > }
> > 
> > The volatile simply forces a load to be emitted.
> 
> Mathieu, what do you think? Are you ok with an atomic_read() for
> checking if a tracepoint is enabled, when jump labels are disabled?

Note, I'm fine with this method too. An atomic_read() is extremely fast.
The worse that it does is to prevent gcc from optimizing a little, which
we already cause it to do due to the asm goto that we use.

-- Steve


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