Re: [PATCH v3 4/4] virtio_net: disable cb aggressively
From: Eric Dumazet <hidden>
Date: 2021-05-26 15:15:18
Also in:
lkml, netdev
On 5/26/21 10:24 AM, Michael S. Tsirkin wrote:
There are currently two cases where we poll TX vq not in response to a callback: start xmit and rx napi. We currently do this with callbacks enabled which can cause extra interrupts from the card. Used not to be a big issue as we run with interrupts disabled but that is no longer the case, and in some cases the rate of spurious interrupts is so high linux detects this and actually kills the interrupt. Fix up by disabling the callbacks before polling the tx vq.
It is not clear why we want to poll TX completions from ndo_start_xmit() in napi mode ? This seems not needed, adding costs to sender thread, this might reduce the ability to use a different cpu for tx completions. Also this will likely conflict with BQL model if we want to use BQL at some point.
This probably needs a Fixes: tag
quoted hunk ↗ jump to hunk
Signed-off-by: Michael S. Tsirkin <mst@redhat.com> --- drivers/net/virtio_net.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index c29f42d1e04f..a83dc038d8af 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c@@ -1433,7 +1433,10 @@ static void virtnet_poll_cleantx(struct receive_queue *rq) return; if (__netif_tx_trylock(txq)) { - free_old_xmit_skbs(sq, true); + do { + virtqueue_disable_cb(sq->vq); + free_old_xmit_skbs(sq, true); + } while (unlikely(!virtqueue_enable_cb_delayed(sq->vq))); if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS) netif_tx_wake_queue(txq);@@ -1605,12 +1608,17 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev) struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum); bool kick = !netdev_xmit_more(); bool use_napi = sq->napi.weight; + unsigned int bytes = skb->len; /* Free up any pending old buffers before queueing new ones. */ - free_old_xmit_skbs(sq, false); + do { + if (use_napi) + virtqueue_disable_cb(sq->vq); - if (use_napi && kick) - virtqueue_enable_cb_delayed(sq->vq); + free_old_xmit_skbs(sq, false); + + } while (use_napi && kick && + unlikely(!virtqueue_enable_cb_delayed(sq->vq))); /* timestamp packet in software */ skb_tx_timestamp(skb);
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