From: David Matlack <dmatlack@google.com>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: linux-kernel@vger.kernel.org, kvm list <kvm@vger.kernel.org>,
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: Re: [PATCH v2 2/4] KVM: X86: Bail out of direct yield in case of under-comitted scenarios
Date: Fri, 14 May 2021 14:32:42 -0700 [thread overview]
Message-ID: <CALzav=e98KRgG+z5oezPmENKDt+NqtEA57ijYh3kMBZyduQUZg@mail.gmail.com> (raw)
In-Reply-To: <1620871189-4763-1-git-send-email-wanpengli@tencent.com>
On Wed, May 12, 2021 at 7:01 PM Wanpeng Li <kernellwp@gmail.com> wrote:
>
> From: Wanpeng Li <wanpengli@tencent.com>
>
> In case of under-comitted 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 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.
>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> 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 9b6bca6..dfb7c32 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;
Since this is a heuristic, do you have any experimental or real world
results that show the benefit?
> +
> rcu_read_lock();
> map = rcu_dereference(vcpu->kvm->arch.apic_map);
>
> --
> 2.7.4
>
next prev parent reply other threads:[~2021-05-14 21:33 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-13 1:59 [PATCH v2 2/4] KVM: X86: Bail out of direct yield in case of under-comitted scenarios Wanpeng Li
2021-05-13 1:59 ` [PATCH v2 3/4] KVM: X86: Fix vCPU preempted state from guest's point of view Wanpeng Li
2021-05-13 1:59 ` [PATCH v2 4/4] KVM: x86: hyper-v: Task srcu lock when accessing kvm_memslots() Wanpeng Li
2021-05-14 21:32 ` David Matlack [this message]
2021-05-17 1:03 ` [PATCH v2 2/4] KVM: X86: Bail out of direct yield in case of under-comitted scenarios Wanpeng Li
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