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Date: Fri, 18 Jan 2013 14:23:29 +0800
From: Jason Wang <jasowang@...hat.com>
To: Wanlong Gao <gaowanlong@...fujitsu.com>
CC: linux-kernel@...r.kernel.org,
Rusty Russell <rusty@...tcorp.com.au>,
"Michael S. Tsirkin" <mst@...hat.com>,
Eric Dumazet <erdnetdev@...il.com>,
virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH V5 2/2] virtio-net: reset virtqueue affinity when doing
cpu hotplug
On 01/18/2013 01:32 PM, 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@...tcorp.com.au>
> Cc: "Michael S. Tsirkin" <mst@...hat.com>
> Cc: Jason Wang <jasowang@...hat.com>
> Cc: Eric Dumazet <erdnetdev@...il.com>
> Cc: virtualization@...ts.linux-foundation.org
> Cc: netdev@...r.kernel.org
> Signed-off-by: Wanlong Gao <gaowanlong@...fujitsu.com>
> ---
> V4->V5:
> New method to deal with the cpu hotplug actions (Rusty)
>
> drivers/net/virtio_net.c | 50 ++++++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 44 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 440b0eb..061f2c5 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);
> @@ -126,6 +127,9 @@ struct virtnet_info {
>
> /* Per-cpu variable to show the mapping from CPU to virtqueue */
> int __percpu *vq_index;
> +
> + /* CPU hot plug notifier */
> + struct notifier_block nb;
> };
>
> struct skb_vnet_hdr {
> @@ -1016,7 +1020,7 @@ static int virtnet_vlan_rx_kill_vid(struct net_device *dev, u16 vid)
> return 0;
> }
>
> -static void virtnet_set_affinity(struct virtnet_info *vi, bool set)
> +static void virtnet_set_affinity(struct virtnet_info *vi, bool set, long hcpu)
> {
> int i;
> int cpu;
> @@ -1026,7 +1030,8 @@ static void virtnet_set_affinity(struct virtnet_info *vi, bool set)
> * setting the affinity hint to eliminate the contention.
> */
> if ((vi->curr_queue_pairs == 1 ||
> - vi->max_queue_pairs != num_online_cpus()) && set) {
> + vi->max_queue_pairs != num_online_cpus() - ((hcpu == -1) ? 0 : 1))
> + && set) {
> if (vi->affinity_hint_set)
> set = false;
> else
This make complex the this function. How about introduce another
function that just clean the affinity of cpu during CPU_DOWN_PREPARE.
Then we could get a simpler virtnet_set_affinity() called in CPU_DEAD
like you previous version?
> @@ -1036,6 +1041,8 @@ static void virtnet_set_affinity(struct virtnet_info *vi, bool set)
> if (set) {
> i = 0;
> for_each_online_cpu(cpu) {
> + if (cpu == hcpu)
> + continue;
> virtqueue_set_affinity(vi->rq[i].vq, cpu);
> virtqueue_set_affinity(vi->sq[i].vq, cpu);
> *per_cpu_ptr(vi->vq_index, cpu) = i;
> @@ -1050,14 +1057,36 @@ static void virtnet_set_affinity(struct virtnet_info *vi, bool set)
> }
>
> i = 0;
> - for_each_online_cpu(cpu)
> + for_each_online_cpu(cpu) {
> + if (cpu == hcpu)
> + continue;
> *per_cpu_ptr(vi->vq_index, cpu) =
> ++i % vi->curr_queue_pairs;
> + }
>
> vi->affinity_hint_set = false;
> }
> }
>
> +static int virtnet_cpu_callback(struct notifier_block *nfb,
> + unsigned long action, void *hcpu)
> +{
> + struct virtnet_info *vi = container_of(nfb, struct virtnet_info, nb);
> +
> + switch(action & ~CPU_TASKS_FROZEN) {
> + case CPU_ONLINE:
> + case CPU_DOWN_FAILED:
> + virtnet_set_affinity(vi, true, -1);
> + break;
> + case CPU_DOWN_PREPARE:
> + virtnet_set_affinity(vi, true, (long)hcpu);
> + break;
> + default:
> + break;
> + }
> + return NOTIFY_OK;
> +}
> +
> static void virtnet_get_ringparam(struct net_device *dev,
> struct ethtool_ringparam *ring)
> {
> @@ -1105,7 +1134,7 @@ static int virtnet_set_channels(struct net_device *dev,
> netif_set_real_num_rx_queues(dev, queue_pairs);
>
> get_online_cpus();
> - virtnet_set_affinity(vi, true);
> + virtnet_set_affinity(vi, true, -1);
> put_online_cpus();
> }
>
> @@ -1275,7 +1304,7 @@ static void virtnet_del_vqs(struct virtnet_info *vi)
> struct virtio_device *vdev = vi->vdev;
>
> get_online_cpus();
> - virtnet_set_affinity(vi, false);
> + virtnet_set_affinity(vi, false, -1);
> put_online_cpus();
>
> vdev->config->del_vqs(vdev);
> @@ -1400,7 +1429,7 @@ static int init_vqs(struct virtnet_info *vi)
> goto err_free;
>
> get_online_cpus();
> - virtnet_set_affinity(vi, true);
> + virtnet_set_affinity(vi, true, -1);
> put_online_cpus();
>
> return 0;
> @@ -1534,6 +1563,13 @@ static int virtnet_probe(struct virtio_device *vdev)
> }
> }
>
> + vi->nb.notifier_call = &virtnet_cpu_callback;
> + err = register_hotcpu_notifier(&vi->nb);
> + if (err) {
> + pr_debug("virtio_net: registering cpu notifier failed\n");
> + goto free_recv_bufs;
> + }
> +
> /* Assume link up if device can't report link status,
> otherwise get link status from config. */
> if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STATUS)) {
> @@ -1580,6 +1616,8 @@ static void virtnet_remove(struct virtio_device *vdev)
> {
> struct virtnet_info *vi = vdev->priv;
>
> + unregister_hotcpu_notifier(&vi->nb);
> +
> /* Prevent config work handler from accessing the device. */
> mutex_lock(&vi->config_lock);
> vi->config_enable = false;
--
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