Commit 92bab4e7 authored by David S. Miller's avatar David S. Miller
Browse files

Merge branch 'virtio-net-busy-poll' 



Jason Wang says:

====================
rx busy polling support for virtio-net

This series introduces the support for rx busy polling support.  This
was useful for reducing the latency for a kvm guest.  Instead of
introducing new states and spinlocks, this series re-uses NAPI state
to synchonrize between NAPI and busy polling.  This grealy simplified
the codes and reduce the overheads of spinlocks for normal NAPI fast
path.

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 127% improvement:
transaction rate was increased from 8353.33 to 18966.87.

Changes from V2:
- Avoid introducing new states and spinlocks by reusuing the NAPI
  state
- Fix the budget calculation in virtnet_poll()
- Drop patch 1/3 from V2 since it was useless

Changes from V1:
- split the patch info smaller ones
- add more details about test setup/configuration
====================

Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parents 96b3bff4 91815639

drivers/net/virtio_net.c

+61 −6
Original line number Diff line number Diff line
@@ -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);
@@ -521,6 +522,8 @@ 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;
@@ -725,15 +728,12 @@ static void refill_work(struct work_struct *work) 
	}

}



static int virtnet_poll(struct napi_struct *napi, int budget)

static int virtnet_receive(struct receive_queue *rq, int budget)

{

	struct receive_queue *rq =

		container_of(napi, struct receive_queue, napi);

	struct virtnet_info *vi = rq->vq->vdev->priv;

	unsigned int len, received = 0;

	void *buf;

	unsigned int r, len, received = 0;



again:

	while (received < budget &&

	       (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {

		receive_buf(rq, buf, len);
@@ -745,6 +745,18 @@ again: 
			schedule_delayed_work(&vi->refill, 0);

	}



	return received;

}



static int virtnet_poll(struct napi_struct *napi, int budget)

{

	struct receive_queue *rq =

		container_of(napi, struct receive_queue, napi);

	unsigned int r, received = 0;



again:

	received += virtnet_receive(rq, budget - received);



	/* Out of packets? */

	if (received < budget) {

		r = virtqueue_enable_cb_prepare(rq->vq);
@@ -760,6 +772,43 @@ again: 
	return received;

}



#ifdef CONFIG_NET_RX_BUSY_POLL

/* must be called with local_bh_disable()d */

static int virtnet_busy_poll(struct napi_struct *napi)

{

	struct receive_queue *rq =

		container_of(napi, struct receive_queue, napi);

	struct virtnet_info *vi = rq->vq->vdev->priv;

	int r, received = 0, budget = 4;



	if (!(vi->status & VIRTIO_NET_S_LINK_UP))

		return LL_FLUSH_FAILED;



	if (!napi_schedule_prep(napi))

		return LL_FLUSH_BUSY;



	virtqueue_disable_cb(rq->vq);



again:

	received += virtnet_receive(rq, budget);



	r = virtqueue_enable_cb_prepare(rq->vq);

	clear_bit(NAPI_STATE_SCHED, &napi->state);

	if (unlikely(virtqueue_poll(rq->vq, r)) &&

	    napi_schedule_prep(napi)) {

		virtqueue_disable_cb(rq->vq);

		if (received < budget) {

			budget -= received;

			goto again;

		} else {

			__napi_schedule(napi);

		}

	}



	return received;

}

#endif	/* CONFIG_NET_RX_BUSY_POLL */



static int virtnet_open(struct net_device *dev)

{

	struct virtnet_info *vi = netdev_priv(dev);
@@ -1347,6 +1396,9 @@ 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_busy_poll,

#endif

};



static void virtnet_config_changed_work(struct work_struct *work)
@@ -1552,6 +1604,7 @@ 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);
@@ -1853,11 +1906,13 @@ static int virtnet_freeze(struct virtio_device *vdev) 
	netif_device_detach(vi->dev);

	cancel_delayed_work_sync(&vi->refill);



	if (netif_running(vi->dev))

	if (netif_running(vi->dev)) {

		for (i = 0; i < vi->max_queue_pairs; i++) {

			napi_disable(&vi->rq[i].napi);

			napi_hash_del(&vi->rq[i].napi);

			netif_napi_del(&vi->rq[i].napi);

		}

	}



	remove_vq_common(vi);

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