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 v3 2/5] KVM: X86: Bail out of direct yield in case of under-committed scenarios
Date: Mon, 17 May 2021 07:00:25 -0700 [thread overview]
Message-ID: <1621260028-6467-2-git-send-email-wanpengli@tencent.com> (raw)
In-Reply-To: <1621260028-6467-1-git-send-email-wanpengli@tencent.com>
From: Wanpeng Li <wanpengli@tencent.com>
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@tencent.com>
---
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
next prev parent reply other threads:[~2021-05-17 14:01 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-17 14:00 [PATCH v3 1/5] KVM: exit halt polling on need_resched() for both book3s and generic halt-polling Wanpeng Li
2021-05-17 14:00 ` Wanpeng Li [this message]
2021-05-17 14:00 ` [PATCH v3 3/5] KVM: X86: Fix vCPU preempted state from guest's point of view Wanpeng Li
2021-05-17 14:00 ` [PATCH v3 4/5] KVM: x86: hyper-v: Task srcu lock when accessing kvm_memslots() Wanpeng Li
2021-05-17 14:00 ` [PATCH v3 5/5] KVM: LAPIC: Narrow the timer latency between wait_lapic_expire and world switch Wanpeng Li
2021-05-17 17:51 ` Sean Christopherson
2021-05-18 12:03 ` Wanpeng Li
2021-05-17 16:34 ` [PATCH v3 1/5] KVM: exit halt polling on need_resched() for both book3s and generic halt-polling David Matlack
2021-05-18 12:03 ` Wanpeng Li
2021-05-17 18:13 ` Venkatesh Srinivas
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