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

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

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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