linux-kernel - Re: [RFC 00/17] Pile o' entry stack changes

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Message-ID: <CALCETrXztQ+z+pBDz5Ru6y3e_1uf1xaxkVmOuboDE1uX9vL=hw@mail.gmail.com>
Date:   Wed, 6 Sep 2017 17:01:24 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [RFC 00/17] Pile o' entry stack changes

On Wed, Sep 6, 2017 at 3:16 PM, Andi Kleen <andi@...stfloor.org> wrote:
> Andy Lutomirski <luto@...nel.org> writes:
>>
>>  - Lots of people (Linus included) have asked to convert the entry
>>    code to pop registers on exit instead of movqing them off the
>>    stack.  This makes a bunch of progress in that direction.
>
> You should benchmark it on Atoms. Likely it's a regression there
> because they don't have the special PUSH/POP acceleration.

I'm not entirely sure this is a worthwhile reason.  Atom will lose a
few cycles due to POP throughput, but there's a lot less decode
bandwidth needed and we save a cache line or two.

--Andy