[Xen-devel] Re: [PATCH RFC V2 3/5] kvm hypervisor : Add two hypercalls to support pv-ticketlock

[Avi Kivity <avi@xxxxxxxxxx>]

On 10/24/2011 02:27 PM, Srivatsa Vaddagiri wrote:
> Good point. Assuming yield_on_hlt=1, that would allow the vcpu to be put
> to sleep and let other vcpus make progress.
>
> I guess with that change, we can also dropthe need for other hypercall
> introduced in this patch (kvm_pv_kick_cpu_op()). Essentially a vcpu sleeping 
> because of HLT instruction can be woken up by a IPI issued by vcpu releasing a
> lock.

Not if interrupts are disabled.  My original plan was to use NMIs for
wakeups, but it turns out NMIs can be coalesced under certain rare
circumstances; this requires workarounds by the generic NMI code that
make NMIs too slow.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.


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