On Thu, Dec 06, 2018 at 04:17:36PM +0800, Jason Wang wrote:
>
> On 2018/12/6 上午6:54, Michael S. Tsirkin wrote:
> > 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.
>
>
> I've played a similar patch several days before. The tricky part is the mode
> switching between napi and no napi. We should make sure when the packet is
> sent and trakced by BQL, it should be consumed by BQL as well. I did it by
> tracking it through skb->cb. And deal with the freeze by reset the BQL
> status. Patch attached.
>
> But when testing with vhost-net, I don't very a stable performance, it was
> probably because we batch the used ring updating so tx interrupt may come
> randomly. We probably need to implement time bounded coalescing mechanism
> which could be configured from userspace.
>
> Btw, maybe it's time just enable napi TX by default. I get ~10% TCP_RR
> regression on machine without APICv, (haven't found time to test APICv
> machine). But consider it was for correctness, I think it's acceptable? Then
> we can do optimization on top?
>
>
> Thanks
I don't see how it's for correctness to be frank.
What if we just do the bulk free? Does that fix the regression?
>
> > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > ---
> > 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++;
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