Re: [PATCH] Inter-VM shared memory PCI device

Cam Macdonell
2010-03-10T04:38:29Z

On Tue, Mar 9, 2010 at 5:03 PM, Paul Brook <paul@codesourcery.com> wrote:
>> > In a cross environment that becomes extremely hairy.  For example the x86
>> > architecture effectively has an implicit write barrier before every
>> > store, and an implicit read barrier before every load.
>>
>> Btw, x86 doesn't have any implicit barriers due to ordinary loads.
>> Only stores and atomics have implicit barriers, afaik.
>
> As of March 2009[1] Intel guarantees that memory reads occur in order (they
> may only be reordered relative to writes). It appears AMD do not provide this
> guarantee, which could be an interesting problem for heterogeneous migration..
>
> Paul
>
> [*] The most recent docs I have handy. Up to and including Core-2 Duo.
>

Interesting, but what ordering would cause problems that AMD would do
but Intel wouldn't? Wouldn't that ordering cause the same problems
for POSIX shared memory in general (regardless of Qemu) on AMD?

I think shared memory breaks migration anyway.

Cam