On 18/12/2014 04:16, Wu, Feng wrote:
>>> pre-block:
>>> - Add the vCPU to the blocked per-CPU list
>>> - Clear 'SN'
>>
>> Should SN be already clear (and NV set to POSTED_INTR_VECTOR)?
>
> I think the SN bit should be clear here, Adding it here is just to make sure
> SN is clear when vCPU is blocked, so it can receive wakeup notification event later.
Then, please, WARN if the SN bit is set inside the if (vcpu->blocked).
Inside that if you can just add the vCPU to the blocked list on vcpu_put.
>> Can it
>> happen that you go from sched-out to blocked without doing a sched-in first?
>>
>
> I cannot imagine this scenario, can you please be more specific? Thanks a lot!
I cannot either. :) But it would be the case where SN is not cleared.
So we agree that it cannot happen.
>> In fact, if this is possible, what happens if vcpu->preempted &&
>> vcpu->blocked?
>
> In fact, vcpu->preempted && vcpu->blocked happens sometimes, but I think there is
> no issues. Please refer to the following case:
I agree that there should be no issues. But if it can happen, it's better:
1) to separate the handling of preemption and blocking: preemption
handles SN/NV/NDST, blocking handles the wakeup list.
2) to change this
+ } else if (vcpu->blocked) {
+ /*
+ * The vcpu is blocked on the wait queue.
+ * Store the blocked vCPU on the list of the
+ * vcpu->wakeup_cpu, which is the destination
+ * of the wake-up notification event.
to just
}
if (vcpu->blocked) {
...
}
> kvm_vcpu_block()
> -> vcpu->blocked = true;
> -> prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
>
> before schedule() is called, this vcpu is woken up by another guy, so
> the state of the vcpu associated thread is changed to TASK_RUNNING,
> then preemption happens after interrupts or the following schedule() is
> hit, this will call kvm_sched_out(), in which current->state == TASK_RUNNING
> and vcpu->preempted is set to true. So now vcpu->preempted and vcpu->blocked
> are both true. In vmx_vcpu_put(), we will check vcpu->preempted first, so
> the vCPU will not be blocked, and the vcpu->blocked will be set the false in
> vmx_vcpu_load().
>
> But maybe I need do a little change to the vmx_vcpu_load() like below:
>
> /*
> * Delete the vCPU from the related wakeup queue
> * if we are resuming from blocked state
> */
> if (vcpu->blocked) {
> vcpu->blocked = false;
> + /* if wakeup_cpu == -1, the vcpu is currently not blocked on any
> + pCPU, don't need dequeue here */
> + if (vcpu->wakeup_cpu != -1) {
> spin_lock_irqsave(&per_cpu(blocked_vcpu_on_cpu_lock,
> vcpu->wakeup_cpu), flags);
> list_del(&vcpu->blocked_vcpu_list);
> spin_unlock_irqrestore(&per_cpu(blocked_vcpu_on_cpu_lock,
> vcpu->wakeup_cpu), flags);
> vcpu->wakeup_cpu = -1;
> + }
> }
Good idea.
Paolo
> Any ideas about this? Thanks a lot!
>
> Thanks,
> Feng
>
>
> -> schedule();
>
>
>>
>>> - Set 'NV' to POSTED_INTR_WAKEUP_VECTOR
>>>
>>> post-block:
>>> - Remove the vCPU from the per-CPU list
>>
>> Paolo
>>
>>> Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
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