Date: Fri, 5 Jun 2009 07:54:43 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Rusty Russell <rusty@rustcorp.com.au>
cc: Ingo Molnar <mingo@elte.hu>, Nick Piggin <npiggin@suse.de>,
       Jeremy Fitzhardinge <jeremy@goop.org>, "H. Peter Anvin" <hpa@zytor.com>,
       Thomas Gleixner <tglx@linutronix.de>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, Avi Kivity <avi@redhat.com>,
       Arjan van de Ven <arjan@infradead.org>
Subject: Re: [benchmark] 1% performance overhead of paravirt_ops on native
 kernels
In-Reply-To: <200906051416.19311.rusty@rustcorp.com.au>
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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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