Hi, Thank you for the feedback.
On Thu, 2019-02-28 at 11:30 -0500, Willem de Bruijn wrote: > On Thu, Feb 28, 2019 at 10:04 AM Paolo Abeni <[email protected]> wrote: > > Currently packet_pick_tx_queue() is the only caller of > > ndo_select_queue() using a fallback argument other than > > __netdev_pick_tx. > > > > Leveraging rx queue, we can obtain a similar queue selection > > behavior using core helpers. After this change, ndo_select_queue() > > is always invoked with __netdev_pick_tx() as fallback. > > We can change ndo_select_queue() signature in a followup patch, > > dropping an indirect call per transmitted packet in some scenarios > > (e.g. TCP syn and XDP generic xmit) > > > > This changes slightly how af packet queue selection happens when > > PACKET_QDISC_BYPASS is set. It's now more similar to plan dev_queue_xmit() > > tacking in account both XPS and TC mapping. > > > > Signed-off-by: Paolo Abeni <[email protected]> > > --- > > Note: the main goal here is getting rid of the fallback() indirect > > call in the device drivers implementing ndo_select_queue(). We can > > obtain the same result with the INDIRECT_CALL() harness. Both ways > > we need to export __netdev_pick_tx() but here we avoid the need > > for additional branching. > > --- > > include/linux/netdevice.h | 2 ++ > > net/core/dev.c | 5 +++-- > > net/packet/af_packet.c | 9 +++++++-- > > 3 files changed, 12 insertions(+), 4 deletions(-) > > > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h > > index c10b60297d28..29a558bded82 100644 > > --- a/include/linux/netdevice.h > > +++ b/include/linux/netdevice.h > > @@ -2152,6 +2152,8 @@ static inline void netdev_for_each_tx_queue(struct > > net_device *dev, > > &qdisc_xmit_lock_key); \ > > } > > > > +u16 __netdev_pick_tx(struct net_device *dev, struct sk_buff *skb, > > + struct net_device *sb_dev); > > struct netdev_queue *netdev_pick_tx(struct net_device *dev, > > struct sk_buff *skb, > > struct net_device *sb_dev); > > diff --git a/net/core/dev.c b/net/core/dev.c > > index 2b67f2aa59dd..004d1180671a 100644 > > --- a/net/core/dev.c > > +++ b/net/core/dev.c > > @@ -3704,8 +3704,8 @@ u16 dev_pick_tx_cpu_id(struct net_device *dev, struct > > sk_buff *skb, > > } > > EXPORT_SYMBOL(dev_pick_tx_cpu_id); > > > > -static u16 __netdev_pick_tx(struct net_device *dev, struct sk_buff *skb, > > - struct net_device *sb_dev) > > +u16 __netdev_pick_tx(struct net_device *dev, struct sk_buff *skb, > > + struct net_device *sb_dev) > > { > > struct sock *sk = skb->sk; > > int queue_index = sk_tx_queue_get(sk); > > @@ -3729,6 +3729,7 @@ static u16 __netdev_pick_tx(struct net_device *dev, > > struct sk_buff *skb, > > > > return queue_index; > > } > > +EXPORT_SYMBOL(__netdev_pick_tx); > > > > struct netdev_queue *netdev_pick_tx(struct net_device *dev, > > struct sk_buff *skb, > > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c > > index 8376bc1c1508..1f7ae4a34d27 100644 > > --- a/net/packet/af_packet.c > > +++ b/net/packet/af_packet.c > > @@ -285,14 +285,19 @@ static u16 packet_pick_tx_queue(struct sk_buff *skb) > > { > > struct net_device *dev = skb->dev; > > const struct net_device_ops *ops = dev->netdev_ops; > > + int hint = __packet_pick_tx_queue(dev, skb, NULL); > > > > u16 queue_index; > > > > +#ifdef CONFIG_XPS > > + skb->sender_cpu = hint + 1; > > should this not be raw_smp_processor_id() without the modulo by tx queue > count? yes, here sender_cpu is intentionally 'misused' to keep a behavior more similar to the unpatched kernel. I'll drop the modulo in the next iteration. > also, __packet_pick_tx_queue is a one-line wrapper around > dev_pick_tx_cpu_id. If simplifying the entire wrapper can be removed. Yes, ideally that will go with a follow-up patch. dev_pick_tx_cpu_id() is going to loose an argument too, and I'll have to touch this chunk again. I thought that touching it once would reduce noise. > > > > > +#endif > > + skb_record_rx_queue(skb, hint); > > how is this used in the transmit path? __netdev_pick_tx() [no XPS conf in place] -> skb_tx_hash() -> skb_rx_queue_recorded() -> the packet is mapped to (), module tc mappings. > > if (ops->ndo_select_queue) { > > queue_index = ops->ndo_select_queue(dev, skb, NULL, > > - __packet_pick_tx_queue); > > + __netdev_pick_tx); > > queue_index = netdev_cap_txqueue(dev, queue_index); > > } else { > > - queue_index = __packet_pick_tx_queue(dev, skb, NULL); > > + queue_index = __netdev_pick_tx(dev, skb, NULL); > > } > > this now duplicates the core of netdev_pick_tx. I wonder if we can > just call that instead of open coding. > > either by changing to take a struct netdev_queue * (it > only has two callers), or by moving the core into a separate > netdev_pick_tx_core (as __netdev_pick_tx is already used). I tried to minimize the changes in this RFC. I'll go for netdev_pick_tx_core() in the next iteration, if there are no problem with an additional EXPORT_SYMBOL_GPL(). Thanks, Paolo
