linux-kernel - Re: locking/atomic: Introduce atomic_try

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Message-ID: <CA+55aFyGwGqk4hG4LnQFpnRPJO6pA=w_bWu=hWpuGaHGuyC_7A@mail.gmail.com>
Date:   Sat, 25 Mar 2017 11:00:44 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: locking/atomic: Introduce atomic_try_cmpxchg()

On Sat, Mar 25, 2017 at 12:51 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, Mar 24, 2017 at 10:23:29PM +0100, Peter Zijlstra wrote:
>
>> I'll try and redo the patches that landed in tip and see what it does
>> for total vmlinux size somewhere tomorrow.
>
>    text    data     bss     dec     hex filename
> 10726413        4540256  843776 16110445         f5d36d defconfig-build/vmlinux.pre
> 10730509        4540256  843776 16114541         f5e36d defconfig-build/vmlinux.post
>
> :-(

Hmm. But you are comparing against the *broken* version that did the
unconditional store of the result.

You should at least compare against the fixed version with the
conditional store. That's the one that was hard to get good code
generation from, wasn't it?

                        Linus