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Date: Mon, 24 Oct 2011 17:57:34 +0530
From: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
To: Avi Kivity <avi@redhat.com>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        Greg Kroah-Hartman <gregkh@suse.de>, "H. Peter Anvin" <hpa@zytor.com>,
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        Marcelo Tosatti <mtosatti@redhat.com>, Ingo Molnar <mingo@redhat.com>,
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        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH RFC V2 3/5] kvm hypervisor : Add two hypercalls to
 support pv-ticketlock
Message-ID: <20111024122734.GA10634@linux.vnet.ibm.com>
Reply-To: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
References: <20111023190307.16364.35381.sendpatchset@oc5400248562.ibm.com>
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* Avi Kivity <avi@redhat.com> [2011-10-24 12:14:21]:

> > +/*
> > + * kvm_pv_wait_for_kick_op : Block until kicked by either a KVM_HC_KICK_CPU
> > + * hypercall or a event like interrupt.
> > + *
> > + * @vcpu : vcpu which is blocking.
> > + */
> > +static void kvm_pv_wait_for_kick_op(struct kvm_vcpu *vcpu)
> > +{

[snip]

> > +}
> 
> This hypercall can be replaced by a HLT instruction, no?

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.

- vatsa