linux-kernel - Re: [PATCH v9 04/10] x86: refcount: prevent gcc distortions

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Date:   Thu, 4 Oct 2018 13:08:25 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Nadav Amit <namit@...are.com>, Ingo Molnar <mingo@...nel.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jan Beulich <JBeulich@...e.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v9 04/10] x86: refcount: prevent gcc distortions

On 10/04/18 13:05, Nadav Amit wrote:
> 
> Funny. Immediate-patching is what I was playing with when I encountered the
> gcc issue. Performance got worse instead of improving (or at least staying
> the same), because inlining got crazy.
> 
> Anyhow, wait for my soon-to-be-sent RFC in which I define a macro called
> “call” (to reduce the retpoline overhead) before you talk about damage to
> the eyes.
> 

Doing it well is *hard*, as I discovered.  The actual patch is much,
much, larger.

	-hpa