Commit c9b35a6f authored by Li RongQing's avatar Li RongQing Committed by Paolo Bonzini
Browse files

KVM: eventfd: Use synchronize_srcu_expedited() on shutdown 



When hot-unplug a device which has many queues, and guest CPU will has
huge jitter, and unplugging is very slow.

It turns out synchronize_srcu() in irqfd_shutdown() caused the guest
jitter and unplugging latency, so replace synchronize_srcu() with
synchronize_srcu_expedited(), to accelerate the unplugging, and reduce
the guest OS jitter, this accelerates the VM reboot too.

Signed-off-by: default avatarLi RongQing <lirongqing@baidu.com>
Message-ID: <20240711121130.38917-1-lirongqing@baidu.com>
[Call it just once in irqfd_resampler_shutdown. - Paolo]
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 238d3d63

virt/kvm/eventfd.c

+7 −6
Original line number Diff line number Diff line
@@ -97,18 +97,19 @@ irqfd_resampler_shutdown(struct kvm_kernel_irqfd *irqfd) 
	mutex_lock(&kvm->irqfds.resampler_lock);



	list_del_rcu(&irqfd->resampler_link);

	synchronize_srcu(&kvm->irq_srcu);



	if (list_empty(&resampler->list)) {

		list_del_rcu(&resampler->link);

		kvm_unregister_irq_ack_notifier(kvm, &resampler->notifier);

		/*

		 * synchronize_srcu(&kvm->irq_srcu) already called

		 * synchronize_srcu_expedited(&kvm->irq_srcu) already called

		 * in kvm_unregister_irq_ack_notifier().

		 */

		kvm_set_irq(kvm, KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID,

			    resampler->notifier.gsi, 0, false);

		kfree(resampler);

	} else {

		synchronize_srcu_expedited(&kvm->irq_srcu);

	}



	mutex_unlock(&kvm->irqfds.resampler_lock);
@@ -126,7 +127,7 @@ irqfd_shutdown(struct work_struct *work) 
	u64 cnt;



	/* Make sure irqfd has been initialized in assign path. */

	synchronize_srcu(&kvm->irq_srcu);

	synchronize_srcu_expedited(&kvm->irq_srcu);



	/*

	 * Synchronize with the wait-queue and unhook ourselves to prevent
@@ -384,7 +385,7 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) 
		}



		list_add_rcu(&irqfd->resampler_link, &irqfd->resampler->list);

		synchronize_srcu(&kvm->irq_srcu);

		synchronize_srcu_expedited(&kvm->irq_srcu);



		mutex_unlock(&kvm->irqfds.resampler_lock);

	}
@@ -523,7 +524,7 @@ void kvm_unregister_irq_ack_notifier(struct kvm *kvm, 
	mutex_lock(&kvm->irq_lock);

	hlist_del_init_rcu(&kian->link);

	mutex_unlock(&kvm->irq_lock);

	synchronize_srcu(&kvm->irq_srcu);

	synchronize_srcu_expedited(&kvm->irq_srcu);

	kvm_arch_post_irq_ack_notifier_list_update(kvm);

}
@@ -608,7 +609,7 @@ kvm_irqfd_release(struct kvm *kvm) 


/*

 * Take note of a change in irq routing.

 * Caller must invoke synchronize_srcu(&kvm->irq_srcu) afterwards.

 * Caller must invoke synchronize_srcu_expedited(&kvm->irq_srcu) afterwards.

 */

void kvm_irq_routing_update(struct kvm *kvm)

{