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Date: Mon, 4 Nov 2013 14:04:31 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] exec: limit system memory size
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, Marcel Apfelbaum <marcel.a@redhat.com>, Jan Kiszka <jan.kiszka@siemens.com>, qemu-devel@nongnu.org, Andreas =?iso-8859-1?Q?F=E4rber?= <afaerber@suse.de>, Richard Henderson <rth@twiddle.net>

On Mon, Nov 04, 2013 at 12:22:35PM +0100, Paolo Bonzini wrote:
> Il 04/11/2013 12:14, Michael S. Tsirkin ha scritto:
> >> > 
> >> > This patch looks good; however, on top of it can you test 
> >> > kvm-unit-tests with TARGET_PHYS_ADDR_SPACE_BITS=64 and see whether 
> >> > there is a measurable slowdown (in the inl_from_qemu tests)?  If not, 
> >> > we can just get rid of TARGET_PHYS_ADDR_SPACE_BITS in exec.c.
> > I'd rather we fixed a bug first - we need to fix it on stable too - any
> > cleanups can come on top.
> 
> This is not necessarily a cleanup.  Getting rid of
> TARGET_PHYS_ADDR_SPACE_BITS in exec.c means fixing device-to-device DMA
> bugs for example.
> 
> Of course a smaller patch can be done that avoids the renaming of L2_*
> constants.
> 
> > Also, I'm not sure what will this test tell
> > us: inl reads io space, not memory, right?
> 
> The number of levels in the dispatch radix tree is independent of the
> size of the AddressSpace; it is P_L2_LEVELS for both the 64K io space
> and the 2^TARGET_PHYS_ADDRESS_SPACE_BITS memory space.
> 
> Paolo

Hmm I think it's *at most* that deep but can be more shallow, no?

-- 
MST