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From: "Radim Krčmář" <rkrcmar@redhat.com>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	Paolo Bonzini <pbonzini@redhat.com>,
	Liran Alon <liran.alon@oracle.com>
Subject: Re: [PATCH v3 2/3] KVM: X86: Implement PV sched yield hypercall
Date: Mon, 10 Jun 2019 16:17:17 +0200	[thread overview]
Message-ID: <20190610141717.GA6604@flask> (raw)
In-Reply-To: <1559178307-6835-3-git-send-email-wanpengli@tencent.com>

2019-05-30 09:05+0800, Wanpeng Li:
> From: Wanpeng Li <wanpengli@tencent.com>
> 
> The target vCPUs are in runnable state after vcpu_kick and suitable 
> as a yield target. This patch implements the sched yield hypercall.
> 
> 17% performance increasement of ebizzy benchmark can be observed in an 
> over-subscribe environment. (w/ kvm-pv-tlb disabled, testing TLB flush 
> call-function IPI-many since call-function is not easy to be trigged 
> by userspace workload).
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: Liran Alon <liran.alon@oracle.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> @@ -7172,6 +7172,28 @@ void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu)
>  	kvm_x86_ops->refresh_apicv_exec_ctrl(vcpu);
>  }
>  
> +static void kvm_sched_yield(struct kvm *kvm, unsigned long dest_id)
> +{
> +	struct kvm_vcpu *target = NULL;
> +	struct kvm_apic_map *map = NULL;
> +
> +	rcu_read_lock();
> +	map = rcu_dereference(kvm->arch.apic_map);
> +
> +	if (unlikely(!map) || dest_id > map->max_apic_id)
> +		goto out;
> +
> +	if (map->phys_map[dest_id]->vcpu) {

This should check for map->phys_map[dest_id].

> +		target = map->phys_map[dest_id]->vcpu;
> +		rcu_read_unlock();
> +		kvm_vcpu_yield_to(target);
> +	}
> +
> +out:
> +	if (!target)
> +		rcu_read_unlock();

Also, I find the following logic clearer

  {
  	struct kvm_vcpu *target = NULL;
  	struct kvm_apic_map *map;
  	
  	rcu_read_lock();
  	map = rcu_dereference(kvm->arch.apic_map);
  	
  	if (likely(map) && dest_id <= map->max_apic_id && map->phys_map[dest_id])
  		target = map->phys_map[dest_id]->vcpu;
  	
  	rcu_read_unlock();
  	
  	if (target)
  		kvm_vcpu_yield_to(target);
  }

thanks.

  reply	other threads:[~2019-06-10 14:17 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-30  1:05 [PATCH v3 0/3] KVM: Yield to IPI target if necessary Wanpeng Li
2019-05-30  1:05 ` [PATCH v3 1/3] KVM: X86: " Wanpeng Li
2019-05-30  1:05 ` [PATCH v3 2/3] KVM: X86: Implement PV sched yield hypercall Wanpeng Li
2019-06-10 14:17   ` Radim Krčmář [this message]
2019-06-11  8:47     ` Wanpeng Li
2019-05-30  1:05 ` [PATCH v3 3/3] KVM: X86: Expose PV_SCHED_YIELD CPUID feature bit to guest Wanpeng Li
2019-06-10  5:58 ` [PATCH v3 0/3] KVM: Yield to IPI target if necessary Wanpeng Li
2019-06-10 14:34 ` Radim Krčmář
2019-06-11  1:11   ` Sean Christopherson
2019-06-11  1:45     ` Wanpeng Li
2019-06-11  1:48       ` Nadav Amit
2019-06-11 10:02         ` Wanpeng Li
2019-06-11 16:57           ` Nadav Amit
2019-06-12  1:18             ` Wanpeng Li
2019-06-12  1:37               ` Nadav Amit
2019-06-28  9:12                 ` Wanpeng Li
2019-06-28  9:18                   ` Wanpeng Li
2019-06-11 10:26   ` Wanpeng Li

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