linux-kernel - Re: [PATCH 02/11] x86: code shrink in paranoid

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Message-ID: <54DBC344.7090402@zytor.com>
Date:	Wed, 11 Feb 2015 13:01:56 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Denys Vlasenko <dvlasenk@...hat.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/11] x86: code shrink in paranoid_exit

On 02/11/2015 12:36 PM, Andy Lutomirski wrote:
> 
> This is sort of a reply to the wrong thread, but wouldn't it be nicer
> if we could pop a bunch of regs instead of using mov followed by add?
> (Yes, this could be a followup, but it could be easier to spot now by
> changing macros like RESTORE_XYZ.)
> 

As far as I recall, it was an optimization for the Pentium 4 and
possibly K8.  At this point, most CPUs have stack engines so push/pop
may be faster or at least the same speed.  It would be nice to
microbenchmark.

	-hpa


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