From: Andi Kleen <ak@suse.de>
To: Linus Torvalds <torvalds@osdl.org>
Subject: Re: [rfc patch] i386: don't save eflags on task switch
Date: Sun, 5 Nov 2006 06:41:14 +0100
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Cc: Benjamin LaHaise <bcrl@kvack.org>, Zachary Amsden <zach@vmware.com>,
       Chuck Ebbert <76306.1226@compuserve.com>,
       linux-kernel <linux-kernel@vger.kernel.org>
References: <200611040200_MC3-1-D04D-6EA3@compuserve.com> <20061105035556.GQ9057@kvack.org> <Pine.LNX.4.64.0611041959260.25218@g5.osdl.org>
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> 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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