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Subject[PATCH RFC 1/2] virtio-net: bql support
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 <mst@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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