[Xen-users] Give dom0 2 pinned vcpus, but share one with domU

[jumperalex <alex@xxxxxxxxxxxxxx>]

Is it possible to give dom0 two vcpus, pinned, but also allow one of those to
be shared with a domU?

So right now I'm setup like this:
dom0: dom0_max_vcpus=1 dom0_vcpus_pin
archVM: vcpu="1-7"

In most of my use cases this works fine, but in a few (rsync specifically)
my dom0 is just getting hammered and it is slowing a local rsync between
domU data.img and dom0 raid array.

Someone else suggested turning off the md5 check in rsync but I'm not
thrilled about turning off hashing of a backup and I want to see if I can
solve the problem with good provisioning first.

So what if I did this:
dom0: dom0_max_vcpus=*2* dom0_vcpus_pin
archVM: vcpu = "1-7"

So I'm giving dom0 2 vcpus which will be pinned to cores 0,1 but I'm still
allowing archVM access to core 1 but not core 0

Will this even work?

How will Xen deal with dividing up core1's cycles?

If there is contention for core1 will that cause a lot of context switching
between cores 0 and 1 within dom0?  Or will core 1 just be shared ~50/50
while core 0 does dom0's heavy lifting?

I know I could just give archVM 6 cores instead of 7, but I really want it
to have access to as many cores as possible for heavy transcoding loads but
I also know I need to dedicate one to dom0 so this is my compromise
solution.  



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