Re: [PATCH net-next v2 2/5] virtio-net: transmit napi
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date: 2017-04-20 16:03:32
quoted
static int xmit_skb(struct send_queue *sq, struct sk_buff *skb) { struct virtio_net_hdr_mrg_rxbuf *hdr;@@ -1130,9 +1172,11 @@ static netdev_tx_t start_xmit(struct sk_buff *skb,struct net_device *dev) int err; struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum); bool kick = !skb->xmit_more; + bool use_napi = sq->napi.weight; /* Free up any pending old buffers before queueing new ones. */ - free_old_xmit_skbs(sq); + if (!use_napi) + free_old_xmit_skbs(sq);I'm not sure this is best or even correct. Consider we clean xmit packets speculatively in virtnet_poll_tx(), we need call free_old_xmit_skbs() unconditionally. This can also help to reduce the possible of napi rescheduling in virtnet_poll_tx().
Because of the use of trylock there. Absolutely, thanks! Perhaps I should only use trylock in the opportunistic clean path from the rx softirq and full locking in the tx softirq. I previously observed that cleaning here would, counterintuitively, reduce efficiency. It reverted the improvements of cleaning transmit completions from the receive softirq. Going through my data, I did not observe this regression anymore on the latest patchset. Let me test again, with and without the new virtqueue_enable_cb_delayed patch. Perhaps that made a difference.