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Date: Wed, 15 Oct 2014 19:04:20 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
CC: Rusty Russell <rusty@...tcorp.com.au>,
virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH RFC] virtio_net: enable tx interrupt
On 10/15/2014 05:53 AM, Michael S. Tsirkin wrote:
> On newer hosts that support delayed tx interrupts,
> we probably don't have much to gain from orphaning
> packets early.
>
> Based on patch by Jason Wang.
>
> Note: this will likely degrade performance for hosts without event idx
> support. Various fallback options are available, including
> orphaning conditionally.
> Testing TBD.
>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
> drivers/net/virtio_net.c | 119 +++++++++++++++++++++++++++++++++--------------
> 1 file changed, 83 insertions(+), 36 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 6b6e136..62c059d 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -72,6 +72,8 @@ struct send_queue {
>
> /* Name of the send queue: output.$index */
> char name[40];
> +
> + struct napi_struct napi;
> };
>
> /* Internal representation of a receive virtqueue */
> @@ -211,15 +213,38 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
> return p;
> }
>
> +static int free_old_xmit_skbs(struct send_queue *sq, int budget)
> +{
> + struct sk_buff *skb;
> + unsigned int len;
> + struct virtnet_info *vi = sq->vq->vdev->priv;
> + struct virtnet_stats *stats = this_cpu_ptr(vi->stats);
> + int sent = 0;
> +
> + while (sent < budget &&
> + (skb = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> + pr_debug("Sent skb %p\n", skb);
> +
> + u64_stats_update_begin(&stats->tx_syncp);
> + stats->tx_bytes += skb->len;
> + stats->tx_packets++;
> + u64_stats_update_end(&stats->tx_syncp);
> +
> + dev_kfree_skb_any(skb);
> + sent++;
> + }
> +
> + return sent;
> +}
> +
> static void skb_xmit_done(struct virtqueue *vq)
> {
> struct virtnet_info *vi = vq->vdev->priv;
> + struct send_queue *sq = &vi->sq[vq2txq(vq)];
>
> - /* Suppress further interrupts. */
> - virtqueue_disable_cb(vq);
> -
> - /* We were probably waiting for more output buffers. */
> - netif_wake_subqueue(vi->dev, vq2txq(vq));
> + if (napi_schedule_prep(&sq->napi)) {
> + __napi_schedule(&sq->napi);
> + }
> }
>
> static unsigned int mergeable_ctx_to_buf_truesize(unsigned long mrg_ctx)
> @@ -766,6 +791,37 @@ again:
> return received;
> }
>
> +static int virtnet_poll_tx(struct napi_struct *napi, int budget)
> +{
> + struct send_queue *sq =
> + container_of(napi, struct send_queue, napi);
> + struct virtnet_info *vi = sq->vq->vdev->priv;
> + struct netdev_queue *txq = netdev_get_tx_queue(vi->dev, vq2txq(sq->vq));
> + unsigned int r, sent = 0;
> +
> +again:
> + __netif_tx_lock(txq, smp_processor_id());
> + virtqueue_disable_cb(sq->vq);
> + sent += free_old_xmit_skbs(sq, budget - sent);
> +
> + if (sent < budget) {
> + r = virtqueue_enable_cb_prepare(sq->vq);
So even virtqueue_enable_cb_delayed() was used in start_xmit(). This can
move used index backwards to trigger unnecessary interrupts.
> + napi_complete(napi);
> + __netif_tx_unlock(txq);
> + if (unlikely(virtqueue_poll(sq->vq, r)) &&
> + napi_schedule_prep(napi)) {
> + virtqueue_disable_cb(sq->vq);
> + __napi_schedule(napi);
> + goto again;
> + }
> + } else {
> + __netif_tx_unlock(txq);
> + }
> +
> + netif_wake_subqueue(vi->dev, vq2txq(sq->vq));
> + return sent;
> +}
> +
> #ifdef CONFIG_NET_RX_BUSY_POLL
> /* must be called with local_bh_disable()d */
> static int virtnet_busy_poll(struct napi_struct *napi)
> @@ -814,30 +870,12 @@ static int virtnet_open(struct net_device *dev)
> if (!try_fill_recv(&vi->rq[i], GFP_KERNEL))
> schedule_delayed_work(&vi->refill, 0);
> virtnet_napi_enable(&vi->rq[i]);
> + napi_enable(&vi->sq[i].napi);
> }
>
> return 0;
> }
>
> -static void free_old_xmit_skbs(struct send_queue *sq)
> -{
> - struct sk_buff *skb;
> - unsigned int len;
> - struct virtnet_info *vi = sq->vq->vdev->priv;
> - struct virtnet_stats *stats = this_cpu_ptr(vi->stats);
> -
> - while ((skb = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> - pr_debug("Sent skb %p\n", skb);
> -
> - u64_stats_update_begin(&stats->tx_syncp);
> - stats->tx_bytes += skb->len;
> - stats->tx_packets++;
> - u64_stats_update_end(&stats->tx_syncp);
> -
> - dev_kfree_skb_any(skb);
> - }
> -}
> -
> static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
> {
> struct skb_vnet_hdr *hdr;
> @@ -902,7 +940,9 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
> sg_set_buf(sq->sg, hdr, hdr_len);
> num_sg = skb_to_sgvec(skb, sq->sg + 1, 0, skb->len) + 1;
> }
> - return virtqueue_add_outbuf(sq->vq, sq->sg, num_sg, skb, GFP_ATOMIC);
> +
> + return virtqueue_add_outbuf(sq->vq, sq->sg, num_sg, skb,
> + GFP_ATOMIC);
> }
>
> static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> @@ -910,10 +950,9 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> struct virtnet_info *vi = netdev_priv(dev);
> int qnum = skb_get_queue_mapping(skb);
> struct send_queue *sq = &vi->sq[qnum];
> - int err;
> + int err, qsize = virtqueue_get_vring_size(sq->vq);
>
> - /* Free up any pending old buffers before queueing new ones. */
> - free_old_xmit_skbs(sq);
I think we'd better keep this. Since it may the tx skb freeing not
totally depends on the tx interrupt, delayed interrupt may work better
without damage the latency.
> + virtqueue_disable_cb(sq->vq);
>
> /* Try to transmit */
> err = xmit_skb(sq, skb);
> @@ -930,22 +969,20 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> }
> virtqueue_kick(sq->vq);
>
> - /* Don't wait up for transmitted skbs to be freed. */
> - skb_orphan(skb);
> - nf_reset(skb);
> -
> /* Apparently nice girls don't return TX_BUSY; stop the queue
> * before it gets out of hand. Naturally, this wastes entries. */
> if (sq->vq->num_free < 2+MAX_SKB_FRAGS) {
> netif_stop_subqueue(dev, qnum);
> if (unlikely(!virtqueue_enable_cb_delayed(sq->vq))) {
> /* More just got used, free them then recheck. */
> - free_old_xmit_skbs(sq);
> + free_old_xmit_skbs(sq, qsize);
> if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) {
> netif_start_subqueue(dev, qnum);
> virtqueue_disable_cb(sq->vq);
> }
> }
> + } else if (virtqueue_enable_cb_delayed(sq->vq)) {
> + free_old_xmit_skbs(sq, qsize);
> }
>
> return NETDEV_TX_OK;
> @@ -1124,8 +1161,10 @@ static int virtnet_close(struct net_device *dev)
> /* Make sure refill_work doesn't re-enable napi! */
> cancel_delayed_work_sync(&vi->refill);
>
> - for (i = 0; i < vi->max_queue_pairs; i++)
> + for (i = 0; i < vi->max_queue_pairs; i++) {
> napi_disable(&vi->rq[i].napi);
> + napi_disable(&vi->sq[i].napi);
> + }
>
> return 0;
> }
> @@ -1438,8 +1477,10 @@ static void virtnet_free_queues(struct virtnet_info *vi)
> {
> int i;
>
> - for (i = 0; i < vi->max_queue_pairs; i++)
> + for (i = 0; i < vi->max_queue_pairs; i++) {
> netif_napi_del(&vi->rq[i].napi);
> + netif_napi_del(&vi->sq[i].napi);
> + }
>
> kfree(vi->rq);
> kfree(vi->sq);
> @@ -1593,6 +1634,8 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
> netif_napi_add(vi->dev, &vi->rq[i].napi, virtnet_poll,
> napi_weight);
> napi_hash_add(&vi->rq[i].napi);
> + netif_napi_add(vi->dev, &vi->sq[i].napi, virtnet_poll_tx,
> + napi_weight);
>
> 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);
> @@ -1893,8 +1936,10 @@ static int virtnet_freeze(struct virtio_device *vdev)
> if (netif_running(vi->dev)) {
> for (i = 0; i < vi->max_queue_pairs; i++) {
> napi_disable(&vi->rq[i].napi);
> + napi_disable(&vi->sq[i].napi);
> napi_hash_del(&vi->rq[i].napi);
> netif_napi_del(&vi->rq[i].napi);
> + netif_napi_del(&vi->sq[i].napi);
> }
> }
>
> @@ -1919,8 +1964,10 @@ static int virtnet_restore(struct virtio_device *vdev)
> if (!try_fill_recv(&vi->rq[i], GFP_KERNEL))
> schedule_delayed_work(&vi->refill, 0);
>
> - for (i = 0; i < vi->max_queue_pairs; i++)
> + for (i = 0; i < vi->max_queue_pairs; i++) {
> virtnet_napi_enable(&vi->rq[i]);
> + napi_enable(&vi->sq[i].napi);
> + }
> }
>
> netif_device_attach(vi->dev);
--
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