linux-kernel - Re: [PATCH v3 3/4] x86/alternative: Rewrite optimize

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Message-ID: <Y+QJ81i/QL+Cp1bf@hirez.programming.kicks-ass.net>
Date:   Wed, 8 Feb 2023 21:45:39 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andrew.Cooper3@...rix.com
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, mhiramat@...nel.org,
        kirill.shutemov@...ux.intel.com, jpoimboe@...hat.com
Subject: Re: [PATCH v3 3/4] x86/alternative: Rewrite optimize_nops() some

On Wed, Feb 08, 2023 at 09:44:04PM +0100, Peter Zijlstra wrote:
> GNU as seems to go to .nops 12. 13 gives me a single byte nop and a 12.
> That's also exactly the 3 prefix limit, after which some uarchs start
> taking heavy decode penalties.

Oh noes, counting hard. It maxes out at 11, not 12. Sadness.

Instead, lemme go figure out what those alternatives actually are.