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Subject: Re: [RFC PATCH] Tracepoint: introduce tracepoint() API
From: Steven Rostedt <rostedt@goodmis.org>
To: Jason Baron <jbaron@redhat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@elte.hu>,
        Christoph Lameter <cl@linux-foundation.org>
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Date: Thu, 17 Nov 2011 17:27:17 -0500
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On Thu, 2011-11-17 at 16:58 -0500, Jason Baron wrote:

> I brought this issue up a while back, with a very similar patch to what
> Mathieu wrote. Please see:
> 
> http://thread.gmane.org/gmane.linux.kernel/838911

Ah, I remember this now. Mathieu's version is a bit nicer. And we should
only do this for those places that are the problem cases. Basically only
the places that dereference structures, or have other indirections.

> 
> One conclusion from that thread was that it would be nice if gcc could
> optimize the load so that it only happens in the unlikely path. I filed
> a gcc bug for that: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40207,
> but it doesn't seem to be implemented yet...

I agree that this is a compiler issue, but this has been two years and
no progress. Lets go with Mathieu's solution, and we should add a Link:
tag to Jason's patches as well, with a side note that talks about
Jason's previous changes with it.

-- Steve