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

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Date:   Sat, 25 Mar 2017 19:20:23 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.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 11:00:44AM -0700, Linus Torvalds wrote:
> 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
    10730445        4540256  843776 16114477         f5e32d defconfig-build/vmlinux

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

Well, only broken if not used on stack local variables, but yes.

> 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?

Added above, a few bytes smaller than the shiny new one actually.