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

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

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@xxxxxxxxx>
> ---
> 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