[Xen-devel] Re: [patch 14/21] Xen-paravirt: Add XEN config options and disable unsupported config options.

[Keir Fraser <keir@xxxxxxxxxxxxx>]

On 16/2/07 08:37, "Dan Hecht" <dhecht@xxxxxxxxxx> 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


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