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xen-devel
[Xen-devel] Re: [PATCH RFC V2 3/5] kvm hypervisor : Add two hypercalls t
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To: |
Srivatsa Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [PATCH RFC V2 3/5] kvm hypervisor : Add two hypercalls to support pv-ticketlock |
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From: |
Avi Kivity <avi@xxxxxxxxxx> |
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Date: |
Mon, 24 Oct 2011 15:09:25 +0200 |
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Cc: |
Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, Dave Jiang <dave.jiang@xxxxxxxxx>, KVM <kvm@xxxxxxxxxxxxxxx>, Gleb Natapov <gleb@xxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>, x86@xxxxxxxxxx, Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Marcelo Tosatti <mtosatti@xxxxxxxxxx>, Suzuki Poulose <suzuki@xxxxxxxxxxxxxxxxxx>, Xen <xen-devel@xxxxxxxxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Sedat Dilek <sedat.dilek@xxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Yinghai Lu <yinghai@xxxxxxxxxx>, Greg Kroah-Hartman <gregkh@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> |
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Tue, 25 Oct 2011 10:02:09 -0700 |
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<20111023190307.16364.35381.sendpatchset@xxxxxxxxxxxxxxxxxxxx> <20111023190558.16364.2136.sendpatchset@xxxxxxxxxxxxxxxxxxxx> <4EA53A7D.300@xxxxxxxxxx> <20111024122734.GA10634@xxxxxxxxxxxxxxxxxx> |
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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.
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