From c9b35a6f4edea698a5bb4dd8029e7104ee0a3726 Mon Sep 17 00:00:00 2001
From: Li RongQing <lirongqing@baidu.com>
Date: Thu, 11 Jul 2024 20:11:30 +0800
Subject: [PATCH] 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: 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>
---
virt/kvm/eventfd.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 229570059a1bb..992f9beb3e7d0 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -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)
{
--
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