Re: SMP and Xen

[Sarton O'Brien <bsd-xen%roguewrt.org@localhost>]

On Wednesday 03 January 2007 02:52, Steven M. Bellovin wrote:
> I have a dual-processor machine I'm using for Xen.  A few questions...
>
> First -- is it safe to use SMP with Xen?  I've heard contradictory
> opinions on this.  This is Xen3.0.3 on 4.0beta2.

Although this is Manuel's department, I run current and smp works a treat. 
There are still some parts of acpi dmesg reports as not configured but all in 
all it has been stable and robust.

Outstanding issues on my end are:

shutdown -hp does not actually shutdown but -r works fine :)
Consoling a domu can cause it to spin out of control. Can be very frustrating 
when first implementing a domU. Best advice I can give is to enable sshd as 
fast as humanly possible and save regularly! This doesn't happen when under 
the install kernel thankfully.

> Second -- should my Dom0 see both CPUs?  Currently, it does not.

Is this nr_cpus when issuing an 'xm info' ?

xentop should also tell you, as will xm dmesg.

Apparently under linux, a linux domu may see both cpus but not under 
netbsd/xen. I haven't played with linux under smp so don't quote me :)

> Third -- is there any performance benefit to setting 'vcpus' to 2 (for
> a DomU that would benefit from that)?  That is, will a DomU actually
> run on more than one CPU?

My understanding is that it won't run on more than one cpu (netbsd/xen). You 
can force allocation to a particular cpu or allow it to dynamically allocate. 
I've not needed the dedication of a CPU but I can see where this may come in 
handy.

Hopefully someone else can fill in the gaps if there are any. Hope that helps.

Sarton