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

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Date:	Tue, 20 Mar 2007 00:42:48 +0100
From:	Andi Kleen <ak@....de>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	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, zach@...are.com, anthony@...emonkey.ws,
	torvalds@...ux-foundation.org, netdev@...r.kernel.org
Subject: Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable

> Possibly not, but I'd like to be able to say with confidence that
> running a PARAVIRT kernel on bare hardware has no performance loss
> compared to running a !PARAVIRT kernel.  There's the case of small
> instruction sequences which have been replaced with calls (such as
> sti/cli/push;popf/etc), 

My guess is that most critical pushf/popf are in spin_lock_irqsave(). It would 
be possible to special case that one -- inline it -- and use out of line
versions for all the others.

-Andi
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