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

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Message-ID: <c76df3cb3c8944e98baad3406a522bad@AcuMS.aculab.com>
Date:   Wed, 8 Feb 2023 23:04:24 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Andrew.Cooper3@...rix.com'" <Andrew.Cooper3@...rix.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mhiramat@...nel.org" <mhiramat@...nel.org>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>
Subject: RE: [PATCH v3 3/4] x86/alternative: Rewrite optimize_nops() some

From: Andrew.Cooper3@...rix.com
> Sent: 08 February 2023 19:52
...
> Unconditional jmps cost branch prediction these days, and won't be
> successfully predicted until taken.

That is sad :-(

Don't they also use the BTB for the target address?
So even if predicted taken the cpu can speculate from
the wrong address??

	David

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