On 16/2/07 08:37, "Dan Hecht" [off-list ref] wrote:

Hmm?  I thought the periodic timer and one-shot timer both generate the
same VIRQ.  So, how can you mask one without masking the other?

The tickless idle works since the block hypercall disables the periodic
timer.  But for dynticks (aka NO_HZ), you'll need to mask the periodic
timer (even for a running vcpu), while keeping the one-shot timer
unmasked.  I don't think Xen provides an interface to do that.

There's no interface for this right now, but we can easily add one in a
backward compatible way. This also will not prevent a dyntick kernel from
running on an older Xen -- the guest will then receive to many timer
interrupts, but that should only be a performance concern fixable by
upgrading the hypervisor component of the system.

 -- Keir