linux-kernel - Re: [PATCH v8 09/21] x86/paravirt: Align paravirt thunk functions at 16-byte boundaries

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Message-ID: <20150728152839.GA6737@treble.redhat.com>
Date:	Tue, 28 Jul 2015 10:28:39 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Pedro Alves <palves@...hat.com>,
	Namhyung Kim <namhyung@...il.com>,
	Bernd Petrovitsch <bernd@...rovitsch.priv.at>,
	X86 ML <x86@...nel.org>, live-patching@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 09/21] x86/paravirt: Align paravirt thunk functions at
 16-byte boundaries

On Tue, Jul 28, 2015 at 08:23:04AM -0700, Andy Lutomirski wrote:
> On Tue, Jul 28, 2015 at 7:47 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > Paravirt thunk functions aren't aligned, which can impact performance
> > and is inconsistent with gcc-generated functions.
> >
> > Align them at 16-byte boundaries to be consistent with gcc functions.
> 
> IMO stackvalidate shouldn't warn about this.  We've discussed dropping
> the alignment requirement entirely, since it seems to have little
> benefit on modern CPUs.

Stackvalidate didn't actually find this alignment issue.  I just noticed
it when fixing the frame pointer issue.  If alignment no longer helps
with performance on modern CPUS, it's fine to drop this patch.

-- 
Josh
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