linux-kernel - Re: [PATCH 2/6] x86: bug: prevent gcc distortions

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Message-ID: <30EDFE9B-CA25-42EE-A57F-E3054B84223E@vmware.com>
Date:   Fri, 18 May 2018 15:46:33 +0000
From:   Nadav Amit <namit@...are.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Denys Vlasenko <dvlasenk@...hat.com>
Subject: Re: [PATCH 2/6] x86: bug: prevent gcc distortions

Borislav Petkov <bp@...en8.de> wrote:

> On Fri, May 18, 2018 at 02:36:21PM +0000, Nadav Amit wrote:
>> I didn’t try too hard to find more affected (micro)benchmarks, but I am
>> pretty sure there are:
> 
> So you being pretty sure there are, doesn't make me go, oh, ok, then,
> this is an uglification we should try to live with. It is still ugly
> with no proven benefit from it.

In case you didn’t read the cover-letter: the patch-set does give a 2%
performance improvement for #PF-MADV_DONTNEED microbenchmark loop.