netdev - Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable

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Message-ID: <20070320200242.GA90774@muc.de>
Date:	Tue, 20 Mar 2007 21:02:42 +0100
From:	Andi Kleen <ak@....de>
To:	Zachary Amsden <zach@...are.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	David Miller <davem@...emloft.net>, mingo@...e.hu,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.osdl.org, xen-devel@...ts.xensource.com,
	chrisw@...s-sol.org, anthony@...emonkey.ws, netdev@...r.kernel.org
Subject: Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable

> Worth it on 32-bit.  On AMD64, probably not.  On Intel 64-bit, maybe, 
> but less important than in P4 days.

Well most of Intel 64bit is P4 -- and Intel is still shipping
millions more of them each quarter.

> This could change character completely if used at the tail of a function 
> where you now have
> 
> sti; 1: ret
> 
> Which generates an interrupt holdoff on the ret, an unusual thing to do.

Unusual yes, but I don't see how it should cause problems. Or do you
have anything specific in mind? 

Worse is probably that on K8 this case might cause a pipeline stall
if there isn't a prefix in front of the ret.

-Andi
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