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Date: Wed, 07 Dec 2011 22:01:44 +0530
From: Raghavendra K T <raghukt@linux.vnet.ibm.com>
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To: Marcelo Tosatti <mtosatti@redhat.com>
CC: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        Greg Kroah-Hartman <gregkh@suse.de>, KVM <kvm@vger.kernel.org>,
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Subject: Re: [PATCH RFC V3 2/4] kvm hypervisor : Add a hypercall to KVM hypervisor
 to support pv-ticketlocks
References: <20111130085921.23386.89708.sendpatchset@oc5400248562.ibm.com> <20111130085959.23386.69166.sendpatchset@oc5400248562.ibm.com> <20111207104849.GA24849@amt.cnet> <4EDF5413.1030107@linux.vnet.ibm.com> <20111207123330.GA32212@amt.cnet>
In-Reply-To: <20111207123330.GA32212@amt.cnet>
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On 12/07/2011 06:03 PM, Marcelo Tosatti wrote:
> On Wed, Dec 07, 2011 at 05:24:59PM +0530, Raghavendra K T wrote:
>> On 12/07/2011 04:18 PM, Marcelo Tosatti wrote:
>> Yes you are right. It was potentially racy and it was harmful too!.
>> I had observed that it was stalling the CPU before I introduced
>> kicked flag.
>>
>> But now,
>>
>> vcpu->kicked = 1  ==>  kvm_make_request(KVM_REQ_UNHALT, vcpu); ==>
>
> Ok, please use a more descriptive name, such as "pvlock_kicked" or
> something.
>

Yes, pvlock_kicked seems good. 'll use same unless something else
flashes.

>>
>> __vcpu_run() ==>  kvm_check_request(KVM_REQ_UNHALT, vcpu) ==>
>>
>> vcpuN->mp_state = KVM_MP_STATE_RUNNABLE; so eventually we will end up
>> in RUNNABLE.
>>
>> Also Avi pointed that, logically kvm_arch_vcpu_ioctl_set_mpstate should
>> be called only in vcpu thread, so after further debugging, I noticed
>> that,  setting vcpuN->mp_state = KVM_MP_STATE_RUNNABLE; is not
>> necessary.
>> I 'll remove that in the next patch. Thanks for pointing.
>
> In fact you don't need kvm_arch_vcpu_ioctl_set_mpstate either, only the
> new "kicked" flag.
>

True indeed, I meant the same.