[PATCH][v2] KVM: VMX: optimize pi_wakeup_handler

[PATCH][v2] KVM: VMX: optimize pi_wakeup_handler

[Li RongQing]

pi_wakeup_handler is used to wakeup the sleep vCPUs by posted irq
list_for_each_entry is used in it, and whose input is other function
per_cpu(), That cause that per_cpu() be invoked at least twice when
there is one sleep vCPU

so optimize pi_wakeup_handler it by reading once and same to per CPU
spinlock

Signed-off-by: Li RongQing <lirongqing@baidu.com>
---
diff v1: move reading the per-cpu variable out of spinlock protection

 arch/x86/kvm/vmx/posted_intr.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
index 5fdabf3..c5c1d31 100644
--- a/arch/x86/kvm/vmx/posted_intr.c
+++ b/arch/x86/kvm/vmx/posted_intr.c
@@ -215,16 +215,17 @@ void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu)
 void pi_wakeup_handler(void)
 {
 	int cpu = smp_processor_id();
+	struct list_head *wakeup_list = &per_cpu(wakeup_vcpus_on_cpu, cpu);
+	raw_spinlock_t *spinlock = &per_cpu(wakeup_vcpus_on_cpu_lock, cpu);
 	struct vcpu_vmx *vmx;
 
-	raw_spin_lock(&per_cpu(wakeup_vcpus_on_cpu_lock, cpu));
-	list_for_each_entry(vmx, &per_cpu(wakeup_vcpus_on_cpu, cpu),
-			    pi_wakeup_list) {
+	raw_spin_lock(spinlock);
+	list_for_each_entry(vmx, wakeup_list, pi_wakeup_list) {
 
 		if (pi_test_on(&vmx->pi_desc))
 			kvm_vcpu_wake_up(&vmx->vcpu);
 	}
-	raw_spin_unlock(&per_cpu(wakeup_vcpus_on_cpu_lock, cpu));
+	raw_spin_unlock(spinlock);
 }
 
 void __init pi_init_cpu(int cpu)
-- 
1.8.3.1

Re: [PATCH][v2] KVM: VMX: optimize pi_wakeup_handler

[Sean Christopherson]

On Wed, Apr 06, 2022, Li RongQing wrote:
> pi_wakeup_handler is used to wakeup the sleep vCPUs by posted irq
> list_for_each_entry is used in it, and whose input is other function
> per_cpu(), That cause that per_cpu() be invoked at least twice when
> there is one sleep vCPU
> 
> so optimize pi_wakeup_handler it by reading once and same to per CPU
> spinlock
> 
> Signed-off-by: Li RongQing <lirongqing@baidu.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@google.com>

答复: [PATCH][v2] KVM: VMX: optimize pi_wakeup_handler

[Li,Rongqing]

> >
> > Signed-off-by: Li RongQing <lirongqing@baidu.com>
> > ---
> 
> Reviewed-by: Sean Christopherson <seanjc@google.com>


Ping

Thanks

-Li

Re: [PATCH][v2] KVM: VMX: optimize pi_wakeup_handler

[Paolo Bonzini]

On 4/6/22 13:25, Li RongQing wrote:
> pi_wakeup_handler is used to wakeup the sleep vCPUs by posted irq
> list_for_each_entry is used in it, and whose input is other function
> per_cpu(), That cause that per_cpu() be invoked at least twice when
> there is one sleep vCPU
> 
> so optimize pi_wakeup_handler it by reading once and same to per CPU
> spinlock
> 
> Signed-off-by: Li RongQing <lirongqing@baidu.com>
> ---
> diff v1: move reading the per-cpu variable out of spinlock protection
> 
>   arch/x86/kvm/vmx/posted_intr.c | 9 +++++----
>   1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
> index 5fdabf3..c5c1d31 100644
> --- a/arch/x86/kvm/vmx/posted_intr.c
> +++ b/arch/x86/kvm/vmx/posted_intr.c
> @@ -215,16 +215,17 @@ void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu)
>   void pi_wakeup_handler(void)
>   {
>   	int cpu = smp_processor_id();
> +	struct list_head *wakeup_list = &per_cpu(wakeup_vcpus_on_cpu, cpu);
> +	raw_spinlock_t *spinlock = &per_cpu(wakeup_vcpus_on_cpu_lock, cpu);
>   	struct vcpu_vmx *vmx;
>   
> -	raw_spin_lock(&per_cpu(wakeup_vcpus_on_cpu_lock, cpu));
> -	list_for_each_entry(vmx, &per_cpu(wakeup_vcpus_on_cpu, cpu),
> -			    pi_wakeup_list) {
> +	raw_spin_lock(spinlock);
> +	list_for_each_entry(vmx, wakeup_list, pi_wakeup_list) {
>   
>   		if (pi_test_on(&vmx->pi_desc))
>   			kvm_vcpu_wake_up(&vmx->vcpu);
>   	}
> -	raw_spin_unlock(&per_cpu(wakeup_vcpus_on_cpu_lock, cpu));
> +	raw_spin_unlock(spinlock);
>   }
>   
>   void __init pi_init_cpu(int cpu)

Queued, thanks.

Paolo