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

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Message-ID: <alpine.LFD.2.01.0906091103080.6847@localhost.localdomain>
Date:	Tue, 9 Jun 2009 11:06:10 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Ingo Molnar <mingo@...e.hu>, Nick Piggin <npiggin@...e.de>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	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 Tue, 9 Jun 2009, H. Peter Anvin wrote:
> 
> A major problem is that distros don't seem to be willing to push 64-bit
> kernels for 32-bit distros.  There are a number of good (and
> not-so-good) reasons why users may want to run a 32-bit userspace, but
> not running a 64-bit kernel on capable hardware is just problematic.

Yeah, that's just stupid. A 64-bit kernel should work well with 32-bit 
tools, and while we've occasionally had compat issues (the intel gfx 
people used to claim that they needed to work with a 32-bit kernel because 
they cared about 32-bit tools), they aren't unfixable or even all _that_ 
common.

And they'd be even less common if the whole "64-bit kernel even if you do 
a 32-bit distro" was more common.

The nice thing about a 64-bit kernel is that you should be able to build 
one even if you don't in general have all the 64-bit libraries. So you 
don't need a full 64-bit development environment, you just need a compiler 
that can generate code for both (and that should be the default on x86 
these days).

			Linus
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