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SubjectRe: [PATCH RFC V6 0/11] Paravirtualized ticketlocks
On 04/01/2012 06:48 PM, Avi Kivity wrote:
> On 03/30/2012 01:07 PM, Raghavendra K T wrote:
>> On 03/29/2012 11:33 PM, Raghavendra K T wrote:
>>> On 03/29/2012 03:28 PM, Avi Kivity wrote:
>>>> On 03/28/2012 08:21 PM, Raghavendra K T wrote:
>>
>>> I really like below ideas. Thanks for that!.
>>>
>>>> - from the PLE handler, don't wake up a vcpu that is sleeping
>>>> because it
>>>> is waiting for a kick
>>>
>>> How about, adding another pass in the beginning of kvm_vcpu_on_spin()
>>> to check if any vcpu is already kicked. This would almost result in
>>> yield_to(kicked_vcpu). IMO this is also worth trying.
>>>
>>> will try above ideas soon.
>>>
>>
>> I have patch something like below in mind to try:
>>
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index d3b98b1..5127668 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -1608,15 +1608,18 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
>> * else and called schedule in __vcpu_run. Hopefully that
>> * VCPU is holding the lock that we need and will release it.
>> * We approximate round-robin by starting at the last boosted VCPU.
>> + * Priority is given to vcpu that are unhalted.
>> */
>> - for (pass = 0; pass< 2&& !yielded; pass++) {
>> + for (pass = 0; pass< 3&& !yielded; pass++) {
>> kvm_for_each_vcpu(i, vcpu, kvm) {
>> struct task_struct *task = NULL;
>> struct pid *pid;
>> - if (!pass&& i< last_boosted_vcpu) {
>> + if (!pass&& !vcpu->pv_unhalted)
>> + continue;
>> + else if (pass == 1&& i< last_boosted_vcpu) {
>> i = last_boosted_vcpu;
>> continue;
>> - } else if (pass&& i> last_boosted_vcpu)
>> + } else if (pass == 2&& i> last_boosted_vcpu)
>> break;
>> if (vcpu == me)
>> continue;
>>
>
> Actually I think this is unneeded. The loops tries to find vcpus that
> are runnable but not running (vcpu_active(vcpu->wq)), and halted vcpus
> don't match this condition.
>

I almost agree. But at corner of my thought,

Suppose there are 8 vcpus runnable out of which 4 of them are kicked
but not running, making yield_to those 4 vcpus would result in better
lock progress. no?

I still have little problem getting PLE setup, here (instead rebasing
patches).
Once I get PLE to get that running, and numbers prove no improvement, I
will drop this idea.



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