linux-kernel - Re: [PATCH] x86/mm: Rip out the TLB benchmarking knob

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Message-ID: <CALCETrUwuFR03g7q9vrthNZ+ObDZbim3UqST4btzJz2ywZD=Zw@mail.gmail.com>
Date:   Sat, 14 Oct 2017 10:01:50 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Andy Lutomirski <luto@...nel.org>,
        "linux-tip-commits@...r.kernel.org" 
        <linux-tip-commits@...r.kernel.org>,
        Roman Kagan <rkagan@...tuozzo.com>,
        Johannes Hirte <johannes.hirte@...enkhaos.de>,
        Borislav Petkov <bp@...e.de>,
        Kees Cook <keescook@...omium.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nadav Amit <nadav.amit@...il.com>,
        Adam Borowski <kilobyte@...band.pl>,
        Rik van Riel <riel@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Markus Trippelsdorf <markus@...ppelsdorf.de>,
        Ingo Molnar <mingo@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Biggers <ebiggers@...gle.com>,
        Brian Gerst <brgerst@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86/mm: Rip out the TLB benchmarking knob

On Sat, Oct 14, 2017 at 5:34 AM, Borislav Petkov <bp@...en8.de> wrote:
> On Sat, Oct 14, 2017 at 03:49:12AM -0700, tip-bot for Andy Lutomirski wrote:
>> Commit-ID:  b956575bed91ecfb136a8300742ecbbf451471ab
>> Gitweb:     https://git.kernel.org/tip/b956575bed91ecfb136a8300742ecbbf451471ab
>> Author:     Andy Lutomirski <luto@...nel.org>
>> AuthorDate: Mon, 9 Oct 2017 09:50:49 -0700
>> Committer:  Ingo Molnar <mingo@...nel.org>
>> CommitDate: Sat, 14 Oct 2017 09:21:24 +0200
>>
>> x86/mm: Flush more aggressively in lazy TLB mode
>
> Andy,
>
> I know you're busy so lemme send out the piece removing the benchmarking
> knob. The good thing is, if you revert this patch, you get the knob back
> so it is actually there for those who wanna do benchmarking :-)
>
> It boots, but please check me nevertheless.

Ingo, please don't apply -- please use the one I just sent instead.

>
> Thx.
>
> ---
> From: Borislav Petkov <bp@...e.de>
> Date: Sat, 14 Oct 2017 14:11:14 +0200
> Subject: [PATCH] x86/mm: Rip out the TLB benchmarking knob
>
> This is not really useful to have it upstream as it is only for
> benchmarking PCID vs !PCID and once the code is settled it will become
> one useless knob.

It's actually for benchmarking the two modes against each other on a
PCID CPU.  It's possible, though rather unlikely, that some workloads
are improved significantly when the knob changed.