linux-kernel - Re: [PATCH] xen: core dom0 support

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Date:	Sun, 8 Mar 2009 23:12:08 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Xen-devel <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH] xen: core dom0 support


* H. Peter Anvin <hpa@...or.com> wrote:

> Ingo Molnar wrote:
> > 
> > Since it's the same kernel image i think the only truly reliable 
> > method would be to reboot between _different_ kernel images: 
> > same instructions but randomly re-align variables both in terms 
> > of absolute address and in terms of relative position to each 
> > other. Plus randomize bootmem allocs and never-gets-freed-really 
> > boot-time allocations.
> > 
> > Really hard to do i think ...
> > 
> 
> Ouch, yeah.
> 
> On the other hand, the numbers made sense to me, so I don't 
> see why there is any reason to distrust them.  They show a 5% 
> overhead with pv_ops enabled, reduced to a 2% overhead with 
> the changed.  That is more or less what would match my 
> intuition from seeing the code.

Yeah - it was Jeremy expressed doubt in the numbers, not me.

And we need to eliminate that 2% as well - 2% is still an awful 
lot of native kernel overhead from a kernel feature that 95%+ of 
users do not make any use of.

	Ingo
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