[PATCH net-next v1 12/19] virtio_net: xsk: tx: support wakeup

Xuan Zhuo
Mon, 16 Oct 2023 12:00:26 -0000

xsk wakeup is used to trigger the logic for xsk xmit by xsk framework or
user.

Virtio-Net does not support to actively generate an interruption, so it
tries to trigger tx NAPI on the tx interrupt cpu.

Consider the effect of cache. When interrupt triggers, it is
generally fixed on a CPU. It is better to start TX Napi on the same
CPU.

Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
---
 drivers/net/virtio/main.c       |  3 ++
 drivers/net/virtio/virtio_net.h |  8 +++++
 drivers/net/virtio/xsk.c        | 57 +++++++++++++++++++++++++++++++++
 drivers/net/virtio/xsk.h        |  1 +
 4 files changed, 69 insertions(+)

diff --git a/drivers/net/virtio/main.c b/drivers/net/virtio/main.c
index a08429bef61f..1a222221352e 100644
--- a/drivers/net/virtio/main.c
+++ b/drivers/net/virtio/main.c
@@ -2066,6 +2066,8 @@ static int virtnet_poll_tx(struct napi_struct *napi, int
budget)
 		return 0;
 	}

+	sq->xsk.last_cpu = smp_processor_id();
+
 	txq = netdev_get_tx_queue(vi->dev, index);
 	__netif_tx_lock(txq, raw_smp_processor_id());
 	virtqueue_disable_cb(sq->vq);
@@ -3770,6 +3772,7 @@ static const struct net_device_ops virtnet_netdev = {
 	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
 	.ndo_bpf		= virtnet_xdp,
 	.ndo_xdp_xmit		= virtnet_xdp_xmit,
+	.ndo_xsk_wakeup         = virtnet_xsk_wakeup,
 	.ndo_features_check	= passthru_features_check,
 	.ndo_get_phys_port_name	= virtnet_get_phys_port_name,
 	.ndo_set_features	= virtnet_set_features,
diff --git a/drivers/net/virtio/virtio_net.h b/drivers/net/virtio/virtio_net.h
index 3bbb1f5baad5..7c72a8bb1813 100644
--- a/drivers/net/virtio/virtio_net.h
+++ b/drivers/net/virtio/virtio_net.h
@@ -101,6 +101,14 @@ struct virtnet_sq {
 		struct xsk_buff_pool __rcu *pool;

 		dma_addr_t hdr_dma_address;
+
+		u32 last_cpu;
+		struct __call_single_data csd;
+
+		/* The lock to prevent the repeat of calling
+		 * smp_call_function_single_async().
+		 */
+		spinlock_t ipi_lock;
 	} xsk;
 };

diff --git a/drivers/net/virtio/xsk.c b/drivers/net/virtio/xsk.c
index 0e775a9d270f..973e783260c3 100644
--- a/drivers/net/virtio/xsk.c
+++ b/drivers/net/virtio/xsk.c
@@ -115,6 +115,60 @@ bool virtnet_xsk_xmit(struct virtnet_sq *sq, struct
xsk_buff_pool *pool,
 	return sent == budget;
 }

+static void virtnet_remote_napi_schedule(void *info)
+{
+	struct virtnet_sq *sq = info;
+
+	virtnet_vq_napi_schedule(&sq->napi, sq->vq);
+}
+
+static void virtnet_remote_raise_napi(struct virtnet_sq *sq)
+{
+	u32 last_cpu, cur_cpu;
+
+	last_cpu = sq->xsk.last_cpu;
+	cur_cpu = get_cpu();
+
+	/* On remote cpu, softirq will run automatically when ipi irq exit. On
+	 * local cpu, smp_call_xxx will not trigger ipi interrupt, then softirq
+	 * cannot be triggered automatically. So Call local_bh_enable after to
+	 * trigger softIRQ processing.
+	 */
+	if (last_cpu == cur_cpu) {
+		local_bh_disable();
+		virtnet_vq_napi_schedule(&sq->napi, sq->vq);
+		local_bh_enable();
+	} else {
+		if (spin_trylock(&sq->xsk.ipi_lock)) {
+			smp_call_function_single_async(last_cpu, &sq->xsk.csd);
+			spin_unlock(&sq->xsk.ipi_lock);
+		}
+	}
+
+	put_cpu();
+}
+
+int virtnet_xsk_wakeup(struct net_device *dev, u32 qid, u32 flag)
+{
+	struct virtnet_info *vi = netdev_priv(dev);
+	struct virtnet_sq *sq;
+
+	if (!netif_running(dev))
+		return -ENETDOWN;
+
+	if (qid >= vi->curr_queue_pairs)
+		return -EINVAL;
+
+	sq = &vi->sq[qid];
+
+	if (napi_if_scheduled_mark_missed(&sq->napi))
+		return 0;
+
+	virtnet_remote_raise_napi(sq);
+
+	return 0;
+}
+
 static int virtnet_rq_bind_xsk_pool(struct virtnet_info *vi, struct virtnet_rq
*rq,
 				    struct xsk_buff_pool *pool)
 {
@@ -240,6 +294,9 @@ static int virtnet_xsk_pool_enable(struct net_device *dev,

 	sq->xsk.hdr_dma_address = hdr_dma;

+	INIT_CSD(&sq->xsk.csd, virtnet_remote_napi_schedule, sq);
+	spin_lock_init(&sq->xsk.ipi_lock);
+
 	return 0;

 err_sq:
diff --git a/drivers/net/virtio/xsk.h b/drivers/net/virtio/xsk.h
index 73ca8cd5308b..1bd19dcda649 100644
--- a/drivers/net/virtio/xsk.h
+++ b/drivers/net/virtio/xsk.h
@@ -17,4 +17,5 @@ static inline void *virtnet_xsk_to_ptr(u32 len)
 int virtnet_xsk_pool_setup(struct net_device *dev, struct netdev_bpf *xdp);
 bool virtnet_xsk_xmit(struct virtnet_sq *sq, struct xsk_buff_pool *pool,
 		      int budget);
+int virtnet_xsk_wakeup(struct net_device *dev, u32 qid, u32 flag);
 #endif
--
2.32.0.3.g01195cf9f