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RE: [Xen-devel] Clock interrupts + hypervisor calls


From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of sowmya dayanand
Sent: 28 February 2006 23:10
To: Keir Fraser
Cc: Xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] Clock interrupts + hypervisor calls

My understanding is that
1) There will be only one hypercall at any point of time( there is no queue). Is this right? 
No. In an SMP system there can be more than one Hypercall active at any given time - one per CPU.
2) This hypercall can poll for events/work to do in case it is preemptable. Is there any way that the hypercall can be made non-preemptable? 
Yes, you remove the poll-call. This will of course make the hypercall non-preemptable and it was probably made preemptable for a very good reason [lile somone found that it's working a lot better if you allow preemption at this point], so it's probably not such a great idea to do this.
On 2/28/06, Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> wrote:

On 28 Feb 2006, at 19:22, sowmya dayanand wrote:

> Is there a flag that the long-lived hypercalls set to indicate that
> they can be preempted? Also is the flag per-domain to indicate that
> the hypercall is in progress in the particular domain?

Preemption is voluntary. Long-lived hypercalls poll for pending events
/ work to do.

-- Keir

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