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KVM: x86: Yield to IPI target vCPU only if it is busy

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When sending a call-function IPI-many to vCPUs, yield to the
IPI target vCPU which is marked as preempted.

but when emulating HLT, an idling vCPU will be voluntarily
scheduled out and mark as preempted from the guest kernel
perspective. yielding to idle vCPU is pointless and increase
unnecessary vmexit, maybe miss the true preempted vCPU

so yield to IPI target vCPU only if vCPU is busy and preempted

Signed-off-by: Li RongQing <lirongqing@baidu.com>
Message-Id: <1644380201-29423-1-git-send-email-lirongqing@baidu.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Li RongQing 2022-02-09 12:16:41 +08:00 committed by Paolo Bonzini
parent 92e68cc558
commit 9ee83635d8
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kernel/kvm.c
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@ -624,7 +624,7 @@ static void kvm_smp_send_call_func_ipi(const struct cpumask *mask)
/* Make sure other vCPUs get a chance to run if they need to. */
for_each_cpu(cpu, mask) {
if (vcpu_is_preempted(cpu)) {
if (!idle_cpu(cpu) && vcpu_is_preempted(cpu)) {
kvm_hypercall1(KVM_HC_SCHED_YIELD, per_cpu(x86_cpu_to_apicid, cpu));
break;
}