Re: [PATCH][next] fortify: add branch hints on unlikely fortify_panic paths

[Kees Cook <kees@kernel.org>]

On Wed, Jun 25, 2025 at 05:12:20PM +0100, Colin Ian King wrote:
> Analysis with gcov while running the stress-ng urandom stressor
> shows that there are a couple of fortify panic paths that are highly
> unlikely to be executed for well-behaving code. Adding appropriate
> branch hints improves the stress-ng urandom stressor my a small
> but statistically measureable amount. Ran 100 x 1 minute tests and
> measured the stressor bogo-op rates on a Debian based Intel(R)
> Core(TM) Ultra 9 285K with a 6.15 kernel with turbo disabled to
> reduce jitter.
> 
> Results based on a Geometic Mean of 100 tests:
> 
> Without patch: 50512.95 bogo-ops/sec
> With patch:    50819.58 bogo-ops/sec
> 
> %Std.Deviation of ~0.18%, so low jitter in results, improvement of ~0.6%
> 
> Signed-off-by: Colin Ian King <colin.i.king@gmail.com>

Nice find! It seems some ftrace configs are unhappy with this change,
though?

-Kees

-- 
Kees Cook