Re: [PATCH] x86: Align jump targets to 1 byte boundaries

From: Markus Trippelsdorf
Date: Mon Apr 13 2015 - 12:23:19 EST

On 2015.04.12 at 12:14 +0200, Ingo Molnar wrote:
> In my (past) experience the main win from -flto is not due to better
> hot/cold decisions, but simply due to more aggressive dead code
> elimination. -flto has less of an effect on code that is actually
> being executed.
> Which isn't to be sneered at, but it's far less of a direct effect as
> branch probabilities are, which cut to the core of most hotpaths in
> the kernel.

I did some measurements with gcc-5.1-RC on X86_64 using Andi's latest
LTO kernel patch for 4.0. With my simple monolithic .config the code
size savings are below 1%. That is lower than I've expected.

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