linux-kernel - Re: [PATCH v2 1/4] x86: Use the default ABI for the 32-bit vDSO

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Message-ID: <CALCETrXOrJPidKSAshwE94wumnWqZdwDQ0+fWAY8UZxLf+PCdw@mail.gmail.com>
Date:	Fri, 28 Feb 2014 12:19:34 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Stefani Seibold <stefani@...bold.net>, X86 ML <x86@...nel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	John Stultz <john.stultz@...aro.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	andriy.shevchenko@...ux.intel.com, Martin.Runge@...de-schwarz.com,
	Andreas.Brief@...de-schwarz.com
Subject: Re: [PATCH v2 1/4] x86: Use the default ABI for the 32-bit vDSO

On Fri, Feb 28, 2014 at 7:06 AM, H. Peter Anvin <hpa@...or.com> wrote:
> How many internal function calls are there? It seems we should try to avoid those as much as possible by suitable inlining.

There are no non-static calls at all, except for __x86.get_pc_thunk.
I imagine that gcc is smart enough to improve the calling convention
to non-externally-visible functions.

Amazingly (to me, anyway), the performance of the 32-bit version seems
to be within 1 ns or so of the 64-bit version on SNB.  I suspect that
Intel has optimized the crap out of these things.

--Andy
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