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KVM: eventfd: Use synchronize_srcu_expedited() on shutdown

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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: Li RongQing <lirongqing@baidu.com>
Message-ID: <20240711121130.38917-1-lirongqing@baidu.com>
[Call it just once in irqfd_resampler_shutdown. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Li RongQing 2024-07-11 20:11:30 +08:00 committed by Paolo Bonzini
parent 238d3d63d1
commit c9b35a6f4e
1 changed files with 7 additions and 6 deletions
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13
virt/kvm/eventfd.c
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@ -97,18 +97,19 @@ irqfd_resampler_shutdown(struct kvm_kernel_irqfd *irqfd)
mutex_lock(&kvm->irqfds.resampler_lock); mutex_lock(&kvm->irqfds.resampler_lock);
list_del_rcu(&irqfd->resampler_link); list_del_rcu(&irqfd->resampler_link);
synchronize_srcu(&kvm->irq_srcu);
if (list_empty(&resampler->list)) { if (list_empty(&resampler->list)) {
list_del_rcu(&resampler->link); list_del_rcu(&resampler->link);
kvm_unregister_irq_ack_notifier(kvm, &resampler->notifier); 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(). * in kvm_unregister_irq_ack_notifier().
*/ */
kvm_set_irq(kvm, KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID, kvm_set_irq(kvm, KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID,
resampler->notifier.gsi, 0, false); resampler->notifier.gsi, 0, false);
kfree(resampler); kfree(resampler);
} else {
synchronize_srcu_expedited(&kvm->irq_srcu);
} }
mutex_unlock(&kvm->irqfds.resampler_lock); mutex_unlock(&kvm->irqfds.resampler_lock);
@ -126,7 +127,7 @@ irqfd_shutdown(struct work_struct *work)
u64 cnt; u64 cnt;
/* Make sure irqfd has been initialized in assign path. */ /* 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 * 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); 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); mutex_unlock(&kvm->irqfds.resampler_lock);
} }
@ -523,7 +524,7 @@ void kvm_unregister_irq_ack_notifier(struct kvm *kvm,
mutex_lock(&kvm->irq_lock); mutex_lock(&kvm->irq_lock);
hlist_del_init_rcu(&kian->link); hlist_del_init_rcu(&kian->link);
mutex_unlock(&kvm->irq_lock); 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); 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. * 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) void kvm_irq_routing_update(struct kvm *kvm)
{ {