Re: [PATCH v3 2/3] KVM: X86: Implement PV sched yield hypercall

[Wanpeng Li]

On Mon, 10 Jun 2019 at 22:17, Radim Krčmář  wrote:
>
> 2019-05-30 09:05+0800, Wanpeng Li:
> > From: Wanpeng Li 
> >
> > The target vCPUs are in runnable state after vcpu_kick and suitable
> > as a yield target. This patch implements the sched yield hypercall.
> >
> > 17% performance increasement of ebizzy benchmark can be observed in an
> > over-subscribe environment. (w/ kvm-pv-tlb disabled, testing TLB flush
> > call-function IPI-many since call-function is not easy to be trigged
> > by userspace workload).
> >
> > Cc: Paolo Bonzini 
> > Cc: Radim Krčmář 
> > Cc: Liran Alon 
> > Signed-off-by: Wanpeng Li 
> > ---
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > @@ -7172,6 +7172,28 @@ void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu)
> >   kvm_x86_ops->refresh_apicv_exec_ctrl(vcpu);
> >  }
> >
> > +static void kvm_sched_yield(struct kvm *kvm, unsigned long dest_id)
> > +{
> > + struct kvm_vcpu *target = NULL;
> > + struct kvm_apic_map *map = NULL;
> > +
> > + rcu_read_lock();
> > + map = rcu_dereference(kvm->arch.apic_map);
> > +
> > + if (unlikely(!map) || dest_id > map->max_apic_id)
> > + goto out;
> > +
> > + if (map->phys_map[dest_id]->vcpu) {
>
> This should check for map->phys_map[dest_id].

Yeah, make a mistake here.

>
> > + target = map->phys_map[dest_id]->vcpu;
> > + rcu_read_unlock();
> > + kvm_vcpu_yield_to(target);
> > + }
> > +
> > +out:
> > + if (!target)
> > + rcu_read_unlock();
>
> Also, I find the following logic clearer
>
>   {
> struct kvm_vcpu *target = NULL;
> struct kvm_apic_map *map;
>
> rcu_read_lock();
> map = rcu_dereference(kvm->arch.apic_map);
>
> if (likely(map) && dest_id <= map->max_apic_id && 
> map->phys_map[dest_id])
> target = map->phys_map[dest_id]->vcpu;
>
> rcu_read_unlock();
>
> if (target)
> kvm_vcpu_yield_to(target);
>   }

More better, thanks.

Regards,
Wanpeng Li

Re: [PATCH v3 2/3] KVM: X86: Implement PV sched yield hypercall

[Radim Krčmář]

2019-05-30 09:05+0800, Wanpeng Li:
> From: Wanpeng Li 
> 
> The target vCPUs are in runnable state after vcpu_kick and suitable 
> as a yield target. This patch implements the sched yield hypercall.
> 
> 17% performance increasement of ebizzy benchmark can be observed in an 
> over-subscribe environment. (w/ kvm-pv-tlb disabled, testing TLB flush 
> call-function IPI-many since call-function is not easy to be trigged 
> by userspace workload).
> 
> Cc: Paolo Bonzini 
> Cc: Radim Krčmář 
> Cc: Liran Alon 
> Signed-off-by: Wanpeng Li 
> ---
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> @@ -7172,6 +7172,28 @@ void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu)
>   kvm_x86_ops->refresh_apicv_exec_ctrl(vcpu);
>  }
>  
> +static void kvm_sched_yield(struct kvm *kvm, unsigned long dest_id)
> +{
> + struct kvm_vcpu *target = NULL;
> + struct kvm_apic_map *map = NULL;
> +
> + rcu_read_lock();
> + map = rcu_dereference(kvm->arch.apic_map);
> +
> + if (unlikely(!map) || dest_id > map->max_apic_id)
> + goto out;
> +
> + if (map->phys_map[dest_id]->vcpu) {

This should check for map->phys_map[dest_id].

> + target = map->phys_map[dest_id]->vcpu;
> + rcu_read_unlock();
> + kvm_vcpu_yield_to(target);
> + }
> +
> +out:
> + if (!target)
> + rcu_read_unlock();

Also, I find the following logic clearer

  {
struct kvm_vcpu *target = NULL;
struct kvm_apic_map *map;

rcu_read_lock();
map = rcu_dereference(kvm->arch.apic_map);

if (likely(map) && dest_id <= map->max_apic_id && 
map->phys_map[dest_id])
target = map->phys_map[dest_id]->vcpu;

rcu_read_unlock();

if (target)
kvm_vcpu_yield_to(target);
  }

thanks.

[PATCH v3 2/3] KVM: X86: Implement PV sched yield hypercall

[Wanpeng Li]

From: Wanpeng Li 

The target vCPUs are in runnable state after vcpu_kick and suitable 
as a yield target. This patch implements the sched yield hypercall.

17% performance increasement of ebizzy benchmark can be observed in an 
over-subscribe environment. (w/ kvm-pv-tlb disabled, testing TLB flush 
call-function IPI-many since call-function is not easy to be trigged 
by userspace workload).

Cc: Paolo Bonzini 
Cc: Radim Krčmář 
Cc: Liran Alon 
Signed-off-by: Wanpeng Li 
---
 arch/x86/kvm/x86.c | 26 ++
 1 file changed, 26 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e7e57de..8575b36 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7172,6 +7172,28 @@ void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu)
kvm_x86_ops->refresh_apicv_exec_ctrl(vcpu);
 }
 
+static void kvm_sched_yield(struct kvm *kvm, unsigned long dest_id)
+{
+   struct kvm_vcpu *target = NULL;
+   struct kvm_apic_map *map = NULL;
+
+   rcu_read_lock();
+   map = rcu_dereference(kvm->arch.apic_map);
+
+   if (unlikely(!map) || dest_id > map->max_apic_id)
+   goto out;
+
+   if (map->phys_map[dest_id]->vcpu) {
+   target = map->phys_map[dest_id]->vcpu;
+   rcu_read_unlock();
+   kvm_vcpu_yield_to(target);
+   }
+
+out:
+   if (!target)
+   rcu_read_unlock();
+}
+
 int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 {
unsigned long nr, a0, a1, a2, a3, ret;
@@ -7218,6 +7240,10 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
case KVM_HC_SEND_IPI:
ret = kvm_pv_send_ipi(vcpu->kvm, a0, a1, a2, a3, op_64_bit);
break;
+   case KVM_HC_SCHED_YIELD:
+   kvm_sched_yield(vcpu->kvm, a0);
+   ret = 0;
+   break;
default:
ret = -KVM_ENOSYS;
break;
-- 
2.7.4