Re: [PATCH] KVM: eventfd: Remove redundant synchronize_srcu_expedited from irqfd assignment

[Sean Christopherson <seanjc@google.com>]

On Mon, Mar 09, 2026, lirongqing wrote:
> From: Li RongQing <lirongqing@baidu.com>
> 
> The synchronize_srcu_expedited() call in kvm_irqfd_assign() is unnecessary
> when adding a new irqfd to the resampler list. The list insertion is
> already RCU-safe, and existing readers will either see the old or the
> updated list without inconsistency.

It's not required for kernel safety, but I do think it's required for KVM's ABI,
e.g. to ensure the resampler is visible to readers before KVM_IRQFD returns to
userspace.

> Removing this call reduces latency during resampling irqfd setup.

May I ask why you're micro-optimizing VMs with an in-kernel I/O APIC?

> Signed-off-by: Li RongQing <lirongqing@baidu.com>
> ---
>  virt/kvm/eventfd.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
> index 3201f60..facfeab 100644
> --- a/virt/kvm/eventfd.c
> +++ b/virt/kvm/eventfd.c
> @@ -450,7 +450,6 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
>  		}
>  
>  		list_add_rcu(&irqfd->resampler_link, &irqfd->resampler->list);
> -		synchronize_srcu_expedited(&kvm->irq_srcu);
>  
>  		mutex_unlock(&kvm->irqfds.resampler_lock);
>  	}
> -- 
> 2.9.4
>