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

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Message-Id: <200611050641.14724.ak@suse.de>
Date:	Sun, 5 Nov 2006 06:41:14 +0100
From:	Andi Kleen <ak@...e.de>
To:	Linus Torvalds <torvalds@...l.org>
Cc:	Benjamin LaHaise <bcrl@...ck.org>,
	Zachary Amsden <zach@...are.com>,
	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


> For me, when compiled with -O2, it results in
> 
> 	84
> 	88
> 	132
> 
> which basically says: a "rdtsc->rdtsc" is 84 cycles, putting a "pushfl" in 
> between is another _4_ cycles, and putting a "popfl" in between is about 
> another 48 cycles. 

This means we should definitely change restore_flags() to only STI, 
never popf

-Andi
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