[PATCH RFC 1/2] virtio-net: bql support

[Michael S. Tsirkin]

When use_napi is set, let's enable BQLs.  Note: some of the issues are
similar to wifi.  It's worth considering whether something similar to
commit 36148c2bbfbe ("mac80211: Adjust TSQ pacing shift") might be
benefitial.

Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
---
 drivers/net/virtio_net.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index cecfd77c9f3c..b657bde6b94b 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1325,7 +1325,8 @@ static int virtnet_receive(struct receive_queue *rq, int 
budget,
        return stats.packets;
 }
 
-static void free_old_xmit_skbs(struct send_queue *sq)
+static void free_old_xmit_skbs(struct send_queue *sq, struct netdev_queue *txq,
+                              bool use_napi)
 {
        struct sk_buff *skb;
        unsigned int len;
@@ -1347,6 +1348,9 @@ static void free_old_xmit_skbs(struct send_queue *sq)
        if (!packets)
                return;
 
+       if (use_napi)
+               netdev_tx_completed_queue(txq, packets, bytes);
+
        u64_stats_update_begin(&sq->stats.syncp);
        sq->stats.bytes += bytes;
        sq->stats.packets += packets;
@@ -1364,7 +1368,7 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
                return;
 
        if (__netif_tx_trylock(txq)) {
-               free_old_xmit_skbs(sq);
+               free_old_xmit_skbs(sq, txq, true);
                __netif_tx_unlock(txq);
        }
 
@@ -1440,7 +1444,7 @@ static int virtnet_poll_tx(struct napi_struct *napi, int 
budget)
        struct netdev_queue *txq = netdev_get_tx_queue(vi->dev, vq2txq(sq->vq));
 
        __netif_tx_lock(txq, raw_smp_processor_id());
-       free_old_xmit_skbs(sq);
+       free_old_xmit_skbs(sq, txq, true);
        __netif_tx_unlock(txq);
 
        virtqueue_napi_complete(napi, sq->vq, 0);
@@ -1505,13 +1509,15 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, 
struct net_device *dev)
        struct send_queue *sq = &vi->sq[qnum];
        int err;
        struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
-       bool kick = !skb->xmit_more;
+       bool more = skb->xmit_more;
        bool use_napi = sq->napi.weight;
+       unsigned int bytes = skb->len;
+       bool kick;
 
        /* Free up any pending old buffers before queueing new ones. */
-       free_old_xmit_skbs(sq);
+       free_old_xmit_skbs(sq, txq, use_napi);
 
-       if (use_napi && kick)
+       if (use_napi && !more)
                virtqueue_enable_cb_delayed(sq->vq);
 
        /* timestamp packet in software */
@@ -1552,7 +1558,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct 
net_device *dev)
                if (!use_napi &&
                    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, txq, false);
                        if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) {
                                netif_start_subqueue(dev, qnum);
                                virtqueue_disable_cb(sq->vq);
@@ -1560,7 +1566,12 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, 
struct net_device *dev)
                }
        }
 
-       if (kick || netif_xmit_stopped(txq)) {
+       if (use_napi)
+               kick = __netdev_tx_sent_queue(txq, bytes, more);
+       else
+               kick = !more || netif_xmit_stopped(txq);
+
+       if (kick) {
                if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) 
{
                        u64_stats_update_begin(&sq->stats.syncp);
                        sq->stats.kicks++;
-- 
MST

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