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

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Message-ID: <2176DA84-C064-487F-A062-03A95884F15E@vmware.com>
Date:   Fri, 18 May 2018 16:29:59 +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 03:46:33PM +0000, Nadav Amit wrote:
>> In case you didn’t read the cover-letter: the patch-set does give a 2%
>> performance improvement for #PF-MADV_DONTNEED microbenchmark loop.
> 
> I saw it but *micro*-benchmark doesn't tell me a whole lot. If that
> "improvement" is not visible in real workloads/benchmarks, then I'm just
> as unimpressed.

Funny. I found in my mailbox that you once wrote me: "It is a dumb idea, it
doesn't bring us anything besides some superficial readability which you
don't really need.”

To the point, I think you exaggerate with the effect of the patch on the
code readability: it is not much uglier than it was before, and the change
is in a very specific point in the code.