On Wed, Dec 26, 2012 at 03:06:54PM +0800, Wanlong Gao wrote:
> Add a cpu notifier to virtio-net, so that we can reset the
> virtqueue affinity if the cpu hotplug happens. It improve
> the performance through enabling or disabling the virtqueue
> affinity after doing cpu hotplug.
>
> Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
> Cc: Jason Wang <jasowang@xxxxxxxxxx>
> Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: netdev@xxxxxxxxxxxxxxx
> Signed-off-by: Wanlong Gao <gaowanlong@xxxxxxxxxxxxxx>
Thanks for looking into this.
Some comments:
1. Looks like the logic in
virtnet_set_affinity (and in virtnet_select_queue)
will not work very well when CPU IDs are not
consequitive. This can happen with hot unplug.
Maybe we should add a VQ allocator, and defining
a per-cpu variable specifying the VQ instead
of using CPU ID.
2. The below code seems racy e.g. when CPU is added
during device init.
3. using a global cpu_hotplug seems inelegant.
In any case we should document what is the
meaning of this variable.
> ---
> drivers/net/virtio_net.c | 39 ++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 38 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index a6fcf15..9710cf4 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -26,6 +26,7 @@
> #include <linux/scatterlist.h>
> #include <linux/if_vlan.h>
> #include <linux/slab.h>
> +#include <linux/cpu.h>
>
> static int napi_weight = 128;
> module_param(napi_weight, int, 0444);
> @@ -34,6 +35,8 @@ static bool csum = true, gso = true;
> module_param(csum, bool, 0444);
> module_param(gso, bool, 0444);
>
> +static bool cpu_hotplug = false;
> +
> /* FIXME: MTU in config. */
> #define MAX_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
> #define GOOD_COPY_LEN 128
> @@ -1041,6 +1044,26 @@ static void virtnet_set_affinity(struct virtnet_info *vi, bool set)
> vi->affinity_hint_set = false;
> }
>
> +static int virtnet_cpu_callback(struct notifier_block *nfb,
> + unsigned long action, void *hcpu)
> +{
> + switch(action) {
> + case CPU_ONLINE:
> + case CPU_ONLINE_FROZEN:
> + case CPU_DEAD:
> + case CPU_DEAD_FROZEN:
> + cpu_hotplug = true;
> + break;
> + default:
> + break;
> + }
> + return NOTIFY_OK;
> +}
> +
> +static struct notifier_block virtnet_cpu_notifier = {
> + .notifier_call = virtnet_cpu_callback,
> +};
> +
> static void virtnet_get_ringparam(struct net_device *dev,
> struct ethtool_ringparam *ring)
> {
> @@ -1131,7 +1154,14 @@ static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
> */
> static u16 virtnet_select_queue(struct net_device *dev, struct sk_buff *skb)
> {
> - int txq = skb_rx_queue_recorded(skb) ? skb_get_rx_queue(skb) :
> + int txq;
> +
> + if (unlikely(cpu_hotplug == true)) {
> + virtnet_set_affinity(netdev_priv(dev), true);
> + cpu_hotplug = false;
> + }
> +
> + txq = skb_rx_queue_recorded(skb) ? skb_get_rx_queue(skb) :
> smp_processor_id();
>
> while (unlikely(txq >= dev->real_num_tx_queues))
> @@ -1248,6 +1278,8 @@ static void virtnet_del_vqs(struct virtnet_info *vi)
> {
> struct virtio_device *vdev = vi->vdev;
>
> + unregister_hotcpu_notifier(&virtnet_cpu_notifier);
> +
> virtnet_set_affinity(vi, false);
>
> vdev->config->del_vqs(vdev);
> @@ -1372,6 +1404,11 @@ static int init_vqs(struct virtnet_info *vi)
> goto err_free;
>
> virtnet_set_affinity(vi, true);
> +
> + ret = register_hotcpu_notifier(&virtnet_cpu_notifier);
> + if (ret)
> + goto err_free;
> +
> return 0;
>
> err_free:
> --
> 1.8.0
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