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Date: Tue, 19 Feb 2008 10:28:46 +0100
From: Andi Kleen <andi@firstfloor.org>
To: Willy Tarreau <w@1wt.eu>
Subject: Re: [PATCH 1/3] Fix Unlikely(x) == y
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Cc: Nick Piggin <nickpiggin@yahoo.com.au>, Roel Kluin <12o3l@tiscali.nl>,
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> 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