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Date: Mon, 24 Oct 2011 15:09:25 +0200
From: Avi Kivity <avi@redhat.com>
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To: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
CC: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
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Subject: Re: [PATCH RFC V2 3/5] kvm hypervisor : Add two hypercalls to support
 pv-ticketlock
References: <20111023190307.16364.35381.sendpatchset@oc5400248562.ibm.com> <20111023190558.16364.2136.sendpatchset@oc5400248562.ibm.com> <4EA53A7D.300@redhat.com> <20111024122734.GA10634@linux.vnet.ibm.com>
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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.