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From: Wanpeng Li <kernellwp@gmail.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>
Subject: [PATCH 2/3] KVM: X86: Bail out of direct yield in case of undercomitted scenarios
Date: Sat,  8 May 2021 17:31:49 +0800	[thread overview]
Message-ID: <1620466310-8428-2-git-send-email-wanpengli@tencent.com> (raw)
In-Reply-To: <1620466310-8428-1-git-send-email-wanpengli@tencent.com>

From: Wanpeng Li <wanpengli@tencent.com>

In case of undercomitted scenarios, vCPU can get scheduling easily, 
kvm_vcpu_yield_to adds 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 is such scenarios by checking the length 
of current cpu runqueue.

Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
 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 5bd550e..c0244a6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8358,6 +8358,9 @@ static void kvm_sched_yield(struct kvm_vcpu *vcpu, unsigned long dest_id)
 	struct kvm_vcpu *target = NULL;
 	struct kvm_apic_map *map;
 
+	if (single_task_running())
+		goto no_yield;
+
 	vcpu->stat.directed_yield_attempted++;
 
 	rcu_read_lock();
-- 
2.7.4


  reply	other threads:[~2021-05-08  9:32 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-08  9:31 [PATCH 1/3] KVM: PPC: Book3S HV: exit halt polling on need_resched() as well Wanpeng Li
2021-05-08  9:31 ` Wanpeng Li [this message]
2021-05-11 21:44   ` [PATCH 2/3] KVM: X86: Bail out of direct yield in case of undercomitted scenarios Sean Christopherson
2021-05-12  2:43     ` Wanpeng Li
2021-05-12 16:59       ` Sean Christopherson
2021-05-08  9:31 ` [PATCH 3/3] KVM: X86: Fix vCPU preempted state from guest point of view Wanpeng Li
2021-05-11  0:18   ` Sean Christopherson
2021-05-11 10:28     ` Wanpeng Li
2021-05-12  0:02 ` [PATCH 1/3] KVM: PPC: Book3S HV: exit halt polling on need_resched() as well Wanpeng Li

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