Re: [Qemu-devel] Re: [PATCH] hook cpu running at a higher level.

["Glauber Costa" <glommer@gmail.com>]

On Tue, Dec 30, 2008 at 8:24 AM, Ian Jackson > The Xen qemu process
runs only in one thread which is fine because it
> doesn't need to be involved with actual processor execution.  In
> theory parallel execution (in different threads and thus on different
> physical cpus) of IO emulations requested by different guest vcpus
> might make some small performance difference but I doubt it would be
> worth our while.  So I think the Xen setup will still from qemu's
> point of view look like a single vcpu no matter how many vcpus the
> guest aactually has.

Is it one vcpu or various in lockstep ? If you have only one vcpu,
your main loop can be even simpler than qemu's, which holds them all
in a for loop.

> The way we have approached these problems in the Xen tree is to supply
> an alternative implementation of (say) main_loop and arrange for the
> standard one not to be compiled.  Is it the intent to make kvm a
> run-time selectable option ?  It seems to me that that given that we
> already have different qemu builds for all of the various target
> (guest) cpu architectures, it might be simpler to continue that
> approach.  With a bit of judicious movement of code into appropriate
> files, this will avoid the need for ifs and ifdefs.
>

I believe the idea here is to bring up something close to the accel
patches (this one, plus the ones for memory_rw and registered I
already posted). So you would not see this, but simply
"cpu_main_loop()", that would call into the right thing, no matter
what it is. This allow for both runtime and compile time selection of
what you're running.

-- 
Glauber  Costa.
"Free as in Freedom"
http://glommer.net

"The less confident you are, the more serious you have to act."