On 16/01/2018 14:34, Gal Hammer wrote:
> 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: Marcel Apfelbaum <marcel@xxxxxxxxxx>
> Reviewed-by: Uri Lublin <ulublin@xxxxxxxxxx>
> Signed-off-by: Gal Hammer <ghammer@xxxxxxxxxx>
> ---
> virt/kvm/kvm_main.c | 36 ++++++++++++++++++------------------
> 1 file changed, 18 insertions(+), 18 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 210bf82..1e467fc 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3419,21 +3419,6 @@ 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)
> {
> @@ -3574,7 +3559,9 @@ 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)
> @@ -3588,9 +3575,22 @@ 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);
>
Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
