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Date: Sun, 20 Jul 2014 23:31:11 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: rusty@...tcorp.com.au, virtualization@...ts.linux-foundation.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
Vlad Yasevich <vyasevic@...hat.com>,
Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next V2 3/3] virtio-net: rx busy polling support
On Wed, Jul 16, 2014 at 02:21:47PM +0800, 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.
Pls include data about non polling tests: any effect on
cpu utilization there?
There could be as we are adding locking.
>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Cc: Vlad Yasevich <vyasevic@...hat.com>
> Cc: Eric Dumazet <eric.dumazet@...il.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
> 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 */
do we have to have a new state? no way to reuse the napi state
for this? two lock/unlock operations for a poll seems
excessive.
> };
>
> +#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;
> +
> + 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);
> + return rc;
> +}
> +
> +/* returns true is someone tried to get the rq while napi or refill had it */
s/is/if/
> +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)
let's call it busy poll :)
> +{
> + 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);
Hmm why 4 exactly?
> +
> + 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);
What's going on here, exactly?
> + }
> + }
> }
>
> 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);
> --
> 1.8.3.1
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