linux-kernel - Re: [PATCH] x86/signal: Deinline get

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Message-ID: <560943EF.4040407@redhat.com>
Date:	Mon, 28 Sep 2015 15:43:11 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>
CC:	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...en8.de>,
	Brian Gerst <brgerst@...il.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/signal: Deinline get_sigframe, save 240 bytes

On 09/28/2015 02:33 PM, H. Peter Anvin wrote:
> This one makes me slightly nervous, because it isn't clear
> that these aren't potentially performance sensitive.

CALL instruction is not a crime :)
It costs about the same as one read-modify-write
operation on a memory operand.

This function is used in signal delivery code.
If performance critical code uses massive numbers
of signals, it already has a problem, Unix signals
are too inefficient. That's why we have futexes etc...

> On September 28, 2015 5:23:57 AM PDT, Denys Vlasenko <dvlasenk@...hat.com> wrote:
>> This function compiles to 277 bytes of machine code and has 4
>> callsites.

I must correct myself: there are two callsites, not four.
(There are four calls in the source, but two of them are
in 32-bit code and two are in 64-bit).

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