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Subject[RFC PATCH] virtio-net: reset virtqueue affinity when doing cpu hotplug
Date
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@rustcorp.com.au>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: virtualization@lists.linux-foundation.org
Cc: netdev@vger.kernel.org
Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
---
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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