Re: [PATCH] KVM: VMX: optimize pi_wakeup_handler

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On 4/2/22 06:01, 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 which is safe in
spinlock protection

and same to per CPU spinlock

What's the difference in the generated code?

Paolo

Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
---
  arch/x86/kvm/vmx/posted_intr.c | 12 ++++++++----
  1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
index 5fdabf3..0dae431 100644
--- a/arch/x86/kvm/vmx/posted_intr.c
+++ b/arch/x86/kvm/vmx/posted_intr.c
@@ -214,17 +214,21 @@ void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu)
   */
  void pi_wakeup_handler(void)
  {
+	struct list_head *wakeup_list;
  	int cpu = smp_processor_id();
+	raw_spinlock_t *spinlock;
  	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) {
+	spinlock = &per_cpu(wakeup_vcpus_on_cpu_lock, cpu);
+
+	raw_spin_lock(spinlock);
+	wakeup_list = &per_cpu(wakeup_vcpus_on_cpu, cpu);
+	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)




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