linux-kernel - Re: [PATCH v4 1/5] KVM: exit halt polling on need_resched() for both book3s and generic halt-polling

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Message-ID: <f0247587-e90a-1695-1399-47a67c44d861@redhat.com>
Date:   Mon, 24 May 2021 15:46:43 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Ben Segall <bsegall@...gle.com>,
        Venkatesh Srinivas <venkateshs@...omium.org>,
        David Matlack <dmatlack@...gle.com>,
        Paul Mackerras <paulus@...abs.org>,
        Suraj Jitindar Singh <sjitindarsingh@...il.com>
Subject: Re: [PATCH v4 1/5] KVM: exit halt polling on need_resched() for both
 book3s and generic halt-polling

On 18/05/21 14:00, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@...cent.com>
> 
> Inspired by commit 262de4102c7bb8 (kvm: exit halt polling on need_resched()
> as well), CFS_BANDWIDTH throttling will use resched_task() when there is just
> one task to get the task to block. It was likely allowing VMs to overrun their
> quota when halt polling. Due to PPC implements an arch specific halt polling
> logic, we should add the need_resched() checking there as well. This
> patch adds a helper function that to be shared between book3s and generic
> halt-polling loop.
> 
> Reviewed-by: David Matlack <dmatlack@...gle.com>
> Reviewed-by: Venkatesh Srinivas <venkateshs@...omium.org>
> Cc: Ben Segall <bsegall@...gle.com>
> Cc: Venkatesh Srinivas <venkateshs@...omium.org>
> Cc: Jim Mattson <jmattson@...gle.com>
> Cc: David Matlack <dmatlack@...gle.com>
> Cc: Paul Mackerras <paulus@...abs.org>
> Cc: Suraj Jitindar Singh <sjitindarsingh@...il.com>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---
> v3 -> v4:
>   * rename to kvm_vcpu_can_poll
> v2 -> v3:
>   * add a helper function
> v1 -> v2:
>   * update patch description
> 
>   arch/powerpc/kvm/book3s_hv.c | 2 +-
>   include/linux/kvm_host.h     | 2 ++
>   virt/kvm/kvm_main.c          | 8 ++++++--
>   3 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 28a80d240b76..7360350e66ff 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -3936,7 +3936,7 @@ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
>   				break;
>   			}
>   			cur = ktime_get();
> -		} while (single_task_running() && ktime_before(cur, stop));
> +		} while (kvm_vcpu_can_poll(cur, stop));
>   
>   		spin_lock(&vc->lock);
>   		vc->vcore_state = VCORE_INACTIVE;
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 2f34487e21f2..ba682f738a25 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1583,4 +1583,6 @@ static inline void kvm_handle_signal_exit(struct kvm_vcpu *vcpu)
>   /* Max number of entries allowed for each kvm dirty ring */
>   #define  KVM_DIRTY_RING_MAX_ENTRIES  65536
>   
> +bool kvm_vcpu_can_poll(ktime_t cur, ktime_t stop);
> +
>   #endif
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 6b4feb92dc79..62522c12beba 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2945,6 +2945,11 @@ update_halt_poll_stats(struct kvm_vcpu *vcpu, u64 poll_ns, bool waited)
>   		vcpu->stat.halt_poll_success_ns += poll_ns;
>   }
>   
> +bool kvm_vcpu_can_poll(ktime_t cur, ktime_t stop)
> +{
> +	return single_task_running() && !need_resched() && ktime_before(cur, stop);
> +}
> +
>   /*
>    * The vCPU has executed a HLT instruction with in-kernel mode enabled.
>    */
> @@ -2973,8 +2978,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
>   				goto out;
>   			}
>   			poll_end = cur = ktime_get();
> -		} while (single_task_running() && !need_resched() &&
> -			 ktime_before(cur, stop));
> +		} while (kvm_vcpu_can_poll(cur, stop));
>   	}
>   
>   	prepare_to_rcuwait(&vcpu->wait);
> 

Queued all five, thanks.

Paolo