linux-kernel - Re: [benchmark] 1% performance overhead of paravirt

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Message-ID: <alpine.LFD.2.01.0906050753550.6847@localhost.localdomain>
Date:	Fri, 5 Jun 2009 07:54:43 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
cc:	Ingo Molnar <mingo@...e.hu>, Nick Piggin <npiggin@...e.de>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Avi Kivity <avi@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [benchmark] 1% performance overhead of paravirt_ops on native
 kernels



On Fri, 5 Jun 2009, Rusty Russell wrote:
> 
> Distributions don't ship UP kernels any more; this shows what that costs if 
> you're actually on a UP box.  If we really don't care, perhaps we should make 
> CONFIG_SMP=n an option under EMBEDDED for x86.  And we can rip out the complex 
> patching SMP patching stuff too.

The complex SMP patching is what makes it _possible_ to not ship UP 
kernels any more.

The SMP overhead exists, but it would be even higher if we didn't patch 
things to remove the "lock" prefix.

		Linus
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