Commit d4c67a7a authored by Gal Hammer's avatar Gal Hammer Committed by Radim Krčmář
Browse files

kvm: use insert sort in kvm_io_bus_register_dev function 



The loading time of a VM is quite significant with a CPU usage
reaching 100% when loading a VM that its virtio devices use a
large amount of virt-queues (e.g. a virtio-serial device with
max_ports=511). Most of the time is spend in re-sorting the
kvm_io_bus kvm_io_range array when a new eventfd is registered.

The patch replaces the existing method with an insert sort.

Reviewed-by: default avatarMarcel Apfelbaum <marcel@redhat.com>
Reviewed-by: default avatarUri Lublin <ulublin@redhat.com>
Signed-off-by: default avatarGal Hammer <ghammer@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
parent 01643c51

virt/kvm/kvm_main.c

+18 −18
Original line number Diff line number Diff line
@@ -3398,21 +3398,6 @@ static int kvm_io_bus_sort_cmp(const void *p1, const void *p2) 
	return kvm_io_bus_cmp(p1, p2);

}



static int kvm_io_bus_insert_dev(struct kvm_io_bus *bus, struct kvm_io_device *dev,

			  gpa_t addr, int len)

{

	bus->range[bus->dev_count++] = (struct kvm_io_range) {

		.addr = addr,

		.len = len,

		.dev = dev,

	};



	sort(bus->range, bus->dev_count, sizeof(struct kvm_io_range),

		kvm_io_bus_sort_cmp, NULL);



	return 0;

}



static int kvm_io_bus_get_first_dev(struct kvm_io_bus *bus,

			     gpa_t addr, int len)

{
@@ -3553,7 +3538,9 @@ int kvm_io_bus_read(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, gpa_t addr, 
int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,

			    int len, struct kvm_io_device *dev)

{

	int i;

	struct kvm_io_bus *new_bus, *bus;

	struct kvm_io_range range;



	bus = kvm_get_bus(kvm, bus_idx);

	if (!bus)
@@ -3567,9 +3554,22 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr, 
			  sizeof(struct kvm_io_range)), GFP_KERNEL);

	if (!new_bus)

		return -ENOMEM;

	memcpy(new_bus, bus, sizeof(*bus) + (bus->dev_count *

	       sizeof(struct kvm_io_range)));

	kvm_io_bus_insert_dev(new_bus, dev, addr, len);



	range = (struct kvm_io_range) {

		.addr = addr,

		.len = len,

		.dev = dev,

	};



	for (i = 0; i < bus->dev_count; i++)

		if (kvm_io_bus_cmp(&bus->range[i], &range) > 0)

			break;



	memcpy(new_bus, bus, sizeof(*bus) + i * sizeof(struct kvm_io_range));

	new_bus->dev_count++;

	new_bus->range[i] = range;

	memcpy(new_bus->range + i + 1, bus->range + i,

		(bus->dev_count - i) * sizeof(struct kvm_io_range));

	rcu_assign_pointer(kvm->buses[bus_idx], new_bus);

	synchronize_srcu_expedited(&kvm->srcu);

	kfree(bus);

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