linux-kernel - Re: [rfc patch] i386: don't save eflags on task switch

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Message-Id: <200611051801.18277.ak@suse.de>
Date:	Sun, 5 Nov 2006 18:01:18 +0100
From:	Andi Kleen <ak@...e.de>
To:	Zachary Amsden <zach@...are.com>
Cc:	Linus Torvalds <torvalds@...l.org>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Chuck Ebbert <76306.1226@...puserve.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [rfc patch] i386: don't save eflags on task switch


> sti is expensive as well; iirc just as expensive on most processors as 
> popf, 


On K8 STI is 4 cycles.

> although I don't have hard numbers to back this up on hand.  An  
> _unlikely_ jcc + popf? is better than a sti, for sure, but a likely 
> jcc+popf could cost more than a jcc+sti, depending on model.

99.9999% of all restore_flags just need STI.


-Andi
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