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From: Roland McGrath <roland@redhat.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Jason Baron <jbaron@redhat.com>, linux-kernel@vger.kernel.org,
       mathieu.desnoyers@polymtl.ca, rth@redhat.com
Subject: Re: [PATCH 0/4] RFC: jump label - (tracepoint optimizations)
In-Reply-To: Ingo Molnar's message of  Thursday, 3 September 2009 23:01:39 +0200 <20090903210139.GA25581@elte.hu>
References: <cover.1252007851.git.jbaron@redhat.com>
	<20090903210139.GA25581@elte.hu>
Message-Id: <20090903211142.8490C47C94@magilla.sf.frob.com>
Date: Thu,  3 Sep 2009 14:11:42 -0700 (PDT)
Sender: linux-kernel-owner@vger.kernel.org
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> This looks really interesting and desired. Once GCC adds this (or an 
> equivalent) feature, i'd love to have your optimization in the 
> kernel.

We expect it will be in gcc 4.5 and backported to Fedora's 4.4 pretty soon.
But it's not finalized yet, so we are only doing proof-of-concept so far.

> Basically everything that is optional and touches some very hot 
> codepath would be eligible - not just tracepoints.

Sure.  Any place you have a load+conditional-jump where that is too costly,
we can make it a nop that costs a only cycle or so.  We probably want to
think a little harder about the nicest macro setup we can do to make
employing this trivial in the source.


Thanks,
Roland
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