Re: [Qemu-devel] Re: request : qemu-smp as target

[Paul Brook <paul@codesourcery.com>]

> What inter processor synchronization issues are there?  Could you take
> this a step further and use processes on different machines for each
> processor? (There are many shared memory implementations to choose
> from.)  Are there so many resources shared  
> between the CPUs to make this a ridiculous proposition?

Baically most SMP/shared memory systems assume very low latency communication 
between CPUs and memory. For example on opteron systems remote memory latency 
is of the order of 200 cpu cycles. Typical ethernet latency is several 
million cycles.

To do single-system image over a high latency interconnect (eg. ethernet) you 
need OS and preferably use application support to avoid high-contention 
memory areas. Simulating a SMP system over multiple separate nodes is 
theoretically possible, but performance would probaby be abysmal.

The only solution I can imagine being even vaguely worthwhile is a running 
user-mode qemu on top of a native openmozix system.

> I have ignorantly implemented an SH2 emulator, 

Cool. Any chance you're going to make these changes publicly available?

Paul