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Message-ID: <20080219092846.GB6485@one.firstfloor.org>
Date: Tue, 19 Feb 2008 10:28:46 +0100
From: Andi Kleen <andi@...stfloor.org>
To: Willy Tarreau <w@....eu>
Cc: Nick Piggin <nickpiggin@...oo.com.au>,
Andi Kleen <andi@...stfloor.org>,
Arjan van de Ven <arjan@...radead.org>,
Roel Kluin <12o3l@...cali.nl>, geoffrey.levand@...sony.com,
linuxppc-dev@...abs.org, cbe-oss-dev@...abs.org,
lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] Fix Unlikely(x) == y
> Sometimes, for performance critical paths, I would like gcc to be dumb and
> follow *my* code and not its hard-coded probabilities.
If you really want that, simple: just disable optimization @)
> Maybe one thing we would need would be the ability to assign probabilities
> to each branch based on what we expect, so that gcc could build a better
> tree keeping most frequently used code tight.
Just use profile feedback then for user space. I don't think it's a good
idea for kernel code though because it leads to unreproducible binaries
which would wreck the development model.
> Hmm I've just noticed -fno-guess-branch-probability in the man, I never tried
> it.
Or -fno-reorder-blocks
-Andi
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