From: Wanpeng Li <wanpengli@xxxxxxxxxxx> In case of under-committed scenarios, vCPU can get scheduling easily, kvm_vcpu_yield_to add extra overhead, we can observe a lot of race between vcpu->ready is true and yield fails due to p->state is TASK_RUNNING. Let's bail out in such scenarios by checking the length of current cpu runqueue, it can be treated as a hint of under-committed instead of guarantee of accuracy. The directed_yield_successful/attempted ratio can be improved from 50+% to 80+% in the under-committed scenario. Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx> --- v2 -> v3: * update patch description v1 -> v2: * move the check after attempted counting * update patch description arch/x86/kvm/x86.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 9b6bca616929..dfb7c320581f 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8360,6 +8360,9 @@ static void kvm_sched_yield(struct kvm_vcpu *vcpu, unsigned long dest_id) vcpu->stat.directed_yield_attempted++; + if (single_task_running()) + goto no_yield; + rcu_read_lock(); map = rcu_dereference(vcpu->kvm->arch.apic_map); -- 2.25.1
