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Date: Mon, 04 Nov 2013 12:22:35 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] exec: limit system memory size
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To: "Michael S. Tsirkin" <mst@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, =?ISO-8859-1?Q?Andreas_F=E4rber?= <afaerber@suse.de>, Richard Henderson <rth@twiddle.net>

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