linux-kernel - Re: Performance overhead of paravirt

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Date:	Thu, 21 May 2009 16:10:06 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Chuck Ebbert <cebbert@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	"Xin, Xiaohui" <xiaohui.xin@...el.com>,
	"Li, Xin" <xin.li@...el.com>,
	"Nakajima, Jun" <jun.nakajima@...el.com>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Xen-devel <xen-devel@...ts.xensource.com>
Subject: Re: Performance overhead of paravirt_ops on native identified

Jeremy Fitzhardinge wrote:
> 
> In this specific instance of this example, yes.  But if you start 
> enabling various spinlock debug options then there'll be code following 
> the call.  It would be hard for the runtime patching machinery to know 
> when it would be safe to do the substitution.
> 

"When it is immediately followed by a ret" seems like a straightforward
rule to me?

	-hpa
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