Subject: Re: [PATCH net-next V2 3/3] virtio-net: rx busy polling support

From: Varka Bhadram <[email-masked]>
Date: Wed, 16 Jul 2014 14:08:41 +0530

On 07/16/2014 11:51 AM, Jason Wang wrote:
> Add basic support for rx busy polling.
>
> Test was done between a kvm guest and an external host. Two hosts were
> connected through 40gb mlx4 cards. With both busy_poll and busy_read
> are set to 50 in guest, 1 byte netperf tcp_rr shows 116% improvement:
> transaction rate was increased from 9151.94 to 19787.37.
>
> Cc: Rusty Russell <[email-masked]>
> Cc: Michael S. Tsirkin <[email-masked]>
> Cc: Vlad Yasevich <[email-masked]>
> Cc: Eric Dumazet <[email-masked]>
> Signed-off-by: Jason Wang <[email-masked]>
> ---
>   drivers/net/virtio_net.c | 190 ++++++++++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 187 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index e417d93..4830713 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -27,6 +27,7 @@
>   #include <linux/slab.h>
>   #include <linux/cpu.h>
>   #include <linux/average.h>
> +#include <net/busy_poll.h>
>   
>   static int napi_weight = NAPI_POLL_WEIGHT;
>   module_param(napi_weight, int, 0444);
> @@ -94,8 +95,143 @@ struct receive_queue {
>   
>   	/* Name of this receive queue: input.$index */
>   	char name[40];
> +
> +#ifdef CONFIG_NET_RX_BUSY_POLL
> +	unsigned int state;
> +#define VIRTNET_RQ_STATE_IDLE        0
> +#define VIRTNET_RQ_STATE_NAPI	     1    /* NAPI or refill owns this RQ */
> +#define VIRTNET_RQ_STATE_POLL	     2    /* poll owns this RQ */
> +#define VIRTNET_RQ_STATE_DISABLED    4    /* RQ is disabled */
> +#define VIRTNET_RQ_OWNED (VIRTNET_RQ_STATE_NAPI | VIRTNET_RQ_STATE_POLL)
> +#define VIRTNET_RQ_LOCKED (VIRTNET_RQ_OWNED | VIRTNET_RQ_STATE_DISABLED)
> +#define VIRTNET_RQ_STATE_NAPI_YIELD  8    /* NAPI or refill yielded this RQ */
> +#define VIRTNET_RQ_STATE_POLL_YIELD  16   /* poll yielded this RQ */
> +	spinlock_t lock;
> +#endif  /* CONFIG_NET_RX_BUSY_POLL */
>   };
>   
> +#ifdef CONFIG_NET_RX_BUSY_POLL
> +static inline void virtnet_rq_init_lock(struct receive_queue *rq)
> +{
> +
> +	spin_lock_init(&rq->lock);
> +	rq->state = VIRTNET_RQ_STATE_IDLE;
> +}
> +
> +/* called from the device poll routine or refill routine to get ownership of a
> + * receive queue.
> + */
> +static inline bool virtnet_rq_lock_napi_refill(struct receive_queue *rq)
> +{
> +	int rc = true;
> +

bool instead of int...?

> +	spin_lock(&rq->lock);
> +	if (rq->state & VIRTNET_RQ_LOCKED) {
> +		WARN_ON(rq->state & VIRTNET_RQ_STATE_NAPI);
> +		rq->state |= VIRTNET_RQ_STATE_NAPI_YIELD;
> +		rc = false;
> +	} else
> +		/* we don't care if someone yielded */
> +		rq->state = VIRTNET_RQ_STATE_NAPI;
> +	spin_unlock(&rq->lock);

Lock for rq->state ...?

If yes:
spin_lock(&rq->lock);
if (rq->state & VIRTNET_RQ_LOCKED) {
	rq->state |= VIRTNET_RQ_STATE_NAPI_YIELD;
	spin_unlock(&rq->lock);
	WARN_ON(rq->state & VIRTNET_RQ_STATE_NAPI);
	rc = false;
} else {
	/* we don't care if someone yielded */
	rq->state = VIRTNET_RQ_STATE_NAPI;
	spin_unlock(&rq->lock);
}

> +	return rc;
> +}
> +
> +/* returns true is someone tried to get the rq while napi or refill had it */
> +static inline bool virtnet_rq_unlock_napi_refill(struct receive_queue *rq)
> +{
> +	int rc = false;
> +
> +	spin_lock(&rq->lock);
> +	WARN_ON(rq->state & (VIRTNET_RQ_STATE_POLL |
> +			     VIRTNET_RQ_STATE_NAPI_YIELD));
> +
> +	if (rq->state & VIRTNET_RQ_STATE_POLL_YIELD)
> +		rc = true;
> +	/* will reset state to idle, unless RQ is disabled */
> +	rq->state &= VIRTNET_RQ_STATE_DISABLED;
> +	spin_unlock(&rq->lock);
> +	return rc;
> +}
> +
> +/* called from virtnet_low_latency_recv() */
> +static inline bool virtnet_rq_lock_poll(struct receive_queue *rq)
> +{
> +	int rc = true;
> +
> +	spin_lock_bh(&rq->lock);
> +	if ((rq->state & VIRTNET_RQ_LOCKED)) {
> +		rq->state |= VIRTNET_RQ_STATE_POLL_YIELD;
> +		rc = false;
> +	} else
> +		/* preserve yield marks */
> +		rq->state |= VIRTNET_RQ_STATE_POLL;
> +	spin_unlock_bh(&rq->lock);
> +	return rc;
> +}
> +
> +/* returns true if someone tried to get the receive queue while it was locked */
> +static inline bool virtnet_rq_unlock_poll(struct receive_queue *rq)
> +{
> +	int rc = false;
> +
> +	spin_lock_bh(&rq->lock);
> +	WARN_ON(rq->state & (VIRTNET_RQ_STATE_NAPI));
> +
> +	if (rq->state & VIRTNET_RQ_STATE_POLL_YIELD)
> +		rc = true;
> +	/* will reset state to idle, unless RQ is disabled */
> +	rq->state &= VIRTNET_RQ_STATE_DISABLED;
> +	spin_unlock_bh(&rq->lock);
> +	return rc;
> +}
> +
> +/* return false if RQ is currently owned */
> +static inline bool virtnet_rq_disable(struct receive_queue *rq)
> +{
> +	int rc = true;
> +
> +	spin_lock_bh(&rq->lock);
> +	if (rq->state & VIRTNET_RQ_OWNED)
> +		rc = false;
> +	rq->state |= VIRTNET_RQ_STATE_DISABLED;
> +	spin_unlock_bh(&rq->lock);
> +
> +	return rc;
> +}
> +
> +#else /* CONFIG_NET_RX_BUSY_POLL */
> +static inline void virtnet_rq_init_lock(struct receive_queue *rq)
> +{
> +}
> +
> +static inline bool virtnet_rq_lock_napi_refill(struct receive_queue *rq)
> +{
> +	return true;
> +}
> +
> +static inline bool virtnet_rq_unlock_napi_refill(struct receive_queue *rq)
> +{
> +	return false;
> +}
> +
> +static inline bool virtnet_rq_lock_poll(struct receive_queue *rq)
> +{
> +	return false;
> +}
> +
> +static inline bool virtnet_rq_unlock_poll(struct receive_queue *rq)
> +{
> +	return false;
> +}
> +
> +static inline bool virtnet_rq_disable(struct receive_queue *rq)
> +{
> +	return true;
> +}
> +
> +#endif /* CONFIG_NET_RX_BUSY_POLL */
> +
>   struct virtnet_info {
>   	struct virtio_device *vdev;
>   	struct virtqueue *cvq;
> @@ -521,6 +657,8 @@ static void receive_buf(struct receive_queue *rq, void *buf, unsigned int len)
>   		skb_shinfo(skb)->gso_segs = 0;
>   	}
>   
> +	skb_mark_napi_id(skb, &rq->napi);
> +
>   	netif_receive_skb(skb);
>   	return;
>   
> @@ -714,7 +852,12 @@ static void refill_work(struct work_struct *work)
>   		struct receive_queue *rq = &vi->rq[i];
>   
>   		napi_disable(&rq->napi);
> +		if (!virtnet_rq_lock_napi_refill(rq)) {
> +			virtnet_napi_enable(rq);
> +			continue;
> +		}
>   		still_empty = !try_fill_recv(rq, GFP_KERNEL);
> +		virtnet_rq_unlock_napi_refill(rq);
>   		virtnet_napi_enable(rq);
>   
>   		/* In theory, this can happen: if we don't get any buffers in
> @@ -752,8 +895,13 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
>   	unsigned int r, received = 0;
>   
>   again:
> +	if (!virtnet_rq_lock_napi_refill(rq))
> +		return budget;
> +
>   	received += virtnet_receive(rq, budget);
>   
> +	virtnet_rq_unlock_napi_refill(rq);
> +
>   	/* Out of packets? */
>   	if (received < budget) {
>   		r = virtqueue_enable_cb_prepare(rq->vq);
> @@ -770,20 +918,50 @@ again:
>   	return received;
>   }
>   
> +#ifdef CONFIG_NET_RX_BUSY_POLL
> +/* must be called with local_bh_disable()d */
> +static int virtnet_low_latency_recv(struct napi_struct *napi)
> +{
> +	struct receive_queue *rq =
> +		container_of(napi, struct receive_queue, napi);
> +	struct virtnet_info *vi = rq->vq->vdev->priv;
> +	int received;
> +
> +	if (!(vi->status & VIRTIO_NET_S_LINK_UP))
> +		return LL_FLUSH_FAILED;
> +
> +	if (!virtnet_rq_lock_poll(rq))
> +		return LL_FLUSH_BUSY;
> +
> +	received = virtnet_receive(rq, 4);
> +
> +	virtnet_rq_unlock_poll(rq);
> +
> +	return received;
> +}
> +#endif	/* CONFIG_NET_RX_BUSY_POLL */
> +
>   static void virtnet_napi_enable_all(struct virtnet_info *vi)
>   {
>   	int i;
>   
> -	for (i = 0; i < vi->max_queue_pairs; i++)
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		virtnet_rq_init_lock(&vi->rq[i]);
>   		virtnet_napi_enable(&vi->rq[i]);
> +	}
>   }
>   
>   static void virtnet_napi_disable_all(struct virtnet_info *vi)
>   {
>   	int i;
>   
> -	for (i = 0; i < vi->max_queue_pairs; i++)
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
>   		napi_disable(&vi->rq[i].napi);
> +		while (!virtnet_rq_disable(&vi->rq[i])) {
> +			pr_info("RQ %d locked\n", i);
> +			usleep_range(1000, 20000);
> +		}
> +	}
>   }
>   
>   static int virtnet_open(struct net_device *dev)
> @@ -1372,6 +1550,9 @@ static const struct net_device_ops virtnet_netdev = {
>   #ifdef CONFIG_NET_POLL_CONTROLLER
>   	.ndo_poll_controller = virtnet_netpoll,
>   #endif
> +#ifdef CONFIG_NET_RX_BUSY_POLL
> +	.ndo_busy_poll		= virtnet_low_latency_recv,
> +#endif
>   };
>   
>   static void virtnet_config_changed_work(struct work_struct *work)
> @@ -1577,6 +1758,7 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
>   		vi->rq[i].pages = NULL;
>   		netif_napi_add(vi->dev, &vi->rq[i].napi, virtnet_poll,
>   			       napi_weight);
> +		napi_hash_add(&vi->rq[i].napi);
>   
>   		sg_init_table(vi->rq[i].sg, ARRAY_SIZE(vi->rq[i].sg));
>   		ewma_init(&vi->rq[i].mrg_avg_pkt_len, 1, RECEIVE_AVG_WEIGHT);
> @@ -1880,8 +2062,10 @@ static int virtnet_freeze(struct virtio_device *vdev)
>   
>   	if (netif_running(vi->dev)) {
>   		virtnet_napi_disable_all(vi);
> -		for (i = 0; i < vi->max_queue_pairs; i++)
> +		for (i = 0; i < vi->max_queue_pairs; i++) {
> +			napi_hash_del(&vi->rq[i].napi);
>   			netif_napi_del(&vi->rq[i].napi);
> +		}
>   	}
>   
>   	remove_vq_common(vi);

-- 
Regards,
Varka Bhadram.