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

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Date:	Sun, 7 Jun 2009 10:23:02 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
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>,
	Gerd Knorr <kraxel@...e.de>
Subject: Re: [benchmark] 1% performance overhead of paravirt_ops on native kernels

On Sat, 6 Jun 2009 12:24:43 am Linus Torvalds wrote:
> 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.

"possible"?  You mean "acceptable".  Gray, not black and white.

1) Where's the line?
2) Where are we?  Does patching claw back 5% of the loss?  50%?  90%?

No point benchmarking on my (SMP) laptop for this one.  Gerd cc'd, maybe he 
has benchmarks from when he did the work originally?

Thanks,
Rusty.
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