linux-kernel - Re: [PATCH 1/4] x86: entry.S: tidy up several suboptimal insns

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Message-ID: <20150226075049.0f791b50@grimm.local.home>
Date:	Thu, 26 Feb 2015 07:50:49 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] x86: entry.S: tidy up several suboptimal insns

On Thu, 26 Feb 2015 12:47:03 +0100
Ingo Molnar <mingo@...nel.org> wrote:


> The bona fide removal of a real instruction from a true hot 
> path is generally always worth doing, you don't even have 
> to 'prove' that it improves things: unless the claim is 
> that for some really robust reason the instruction was zero 
> cost to begin with.

I agree that removing instructions from hot paths are for the most part
worth doing without any proof, as long as it doesn't change behavior or
increase the memory footprint. But that's not the case here. If the
change does affect behavior or increases memory footprint, then it
should prove itself as worth doing.

-- Steve
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