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Re: [Xen-devel] [Patch 2 of 2]: PV-domain SMP performance Linux-part

James Harper wrote:
Do you think your changes could be applicable to HVM domains with
appropriately patched kernel spinlock routines?

I had previously wondered about optimizing spinlocks, my idea was
basically for Xen to set a bit in a structure to indicate what vcpus are
currently scheduled, and my modified spinlock acquire routine would
check if the current vcpu wants a spinlock that is held by a currently
unscheduled vcpu, and if so yield to Xen to let the other vcpu schedule.

The only thing I would need from Xen is to know which vcpus were
currently scheduled, the rest would be DomU based.

In a PV domain you can already get that information from the runstate_info structure, which can be mapped into the domain's memory and just read directly. I don't know if its available to an hvm domain, but I don't think it would be hard to implement if it isn't.

   J

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