Re: [PATCH v6 2/3] KVM: dynamic halt_poll_ns adjustment

[Wanpeng Li]

On 9/4/15 9:16 AM, Wanpeng Li wrote:
> [...]
> > > +
> > >   static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
> > >   {
> > >          if (kvm_arch_vcpu_runnable(vcpu)) {
> > > @@ -1929,6 +1963,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
> > >          ktime_t start, cur;
> > >          DEFINE_WAIT(wait);
> > >          bool waited = false;
> > > +       u64 poll_ns = 0, wait_ns = 0, block_ns = 0;
> > >
> > >          start = cur = ktime_get();
> > >          if (vcpu->halt_poll_ns) {
> > > @@ -1941,10 +1976,15 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
> > >                           */
> > >                          if (kvm_vcpu_check_block(vcpu) < 0) {
> > > ++vcpu->stat.halt_successful_poll;
> > > -                               goto out;
> > > +                               break;
> > >                          }
> > >                          cur = ktime_get();
> > >                  } while (single_task_running() && ktime_before(cur, 
> > > stop));
> > > +
> > > +               if (ktime_before(cur, stop)) {
> > You can't use 'cur' to tell if the interrupt arrived. 
> > single_task_running()
> > can break us out of the loop before 'stop'.
> >
> > > +                       poll_ns = ktime_to_ns(cur) - 
> > > ktime_to_ns(start);
> > Put this line before the if(). block_ns should always include the time
> > spent polling; even if polling does not succeed.
>
> Ah, I remember why I keep poll_ns calculation in if(). Actually 
> poll_ns has already been accumulated into wait_ns(see how wait_ns is 
> calculated) if polling does not succeed. If put poll_ns calculation 
> before if() I need to reset variable 'start' to ktime_get().

So how about something like:

@@ -1928,7 +1962,8 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
 {
        ktime_t start, cur;
        DEFINE_WAIT(wait);
-       bool waited = false;
+       bool polled = false, waited = false;
+       u64 poll_ns = 0, wait_ns = 0, block_ns = 0;

        start = cur = ktime_get();
        if (vcpu->halt_poll_ns) {
@@ -1940,11 +1975,17 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
                         * arrives.
                         */
                        if (kvm_vcpu_check_block(vcpu) < 0) {
+                               polled = true;
++vcpu->stat.halt_successful_poll;
-                               goto out;
+                               break;
                        }
                        cur = ktime_get();
                } while (single_task_running() && ktime_before(cur, stop));
+
+               if (polled) {
+                       poll_ns = ktime_to_ns(cur) - ktime_to_ns(start);
+                       goto out;
+               }
        }


Regards,
Wanpeng Li

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