Re: [net-next v10 1/2] net: sched: use queue_mapping to pick tx queue

[Paolo Abeni <pabeni@redhat.com>]

On Tue, 2022-03-15 at 20:48 +0800, Tonghao Zhang wrote:
> On Tue, Mar 15, 2022 at 5:59 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
> > 
> > On 3/14/22 3:15 PM, xiangxia.m.yue@gmail.com wrote:
> > [...]
> > >   include/linux/netdevice.h |  3 +++
> > >   include/linux/rtnetlink.h |  1 +
> > >   net/core/dev.c            | 31 +++++++++++++++++++++++++++++--
> > >   net/sched/act_skbedit.c   |  6 +++++-
> > >   4 files changed, 38 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > > index 0d994710b335..f33fb2d6712a 100644
> > > --- a/include/linux/netdevice.h
> > > +++ b/include/linux/netdevice.h
> > > @@ -3065,6 +3065,9 @@ struct softnet_data {
> > >       struct {
> > >               u16 recursion;
> > >               u8  more;
> > > +#ifdef CONFIG_NET_EGRESS
> > > +             u8  skip_txqueue;
> > > +#endif
> > >       } xmit;
> > >   #ifdef CONFIG_RPS
> > >       /* input_queue_head should be written by cpu owning this struct,
> > > diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
> > > index 7f970b16da3a..ae2c6a3cec5d 100644
> > > --- a/include/linux/rtnetlink.h
> > > +++ b/include/linux/rtnetlink.h
> > > @@ -100,6 +100,7 @@ void net_dec_ingress_queue(void);
> > >   #ifdef CONFIG_NET_EGRESS
> > >   void net_inc_egress_queue(void);
> > >   void net_dec_egress_queue(void);
> > > +void netdev_xmit_skip_txqueue(bool skip);
> > >   #endif
> > > 
> > >   void rtnetlink_init(void);
> > > diff --git a/net/core/dev.c b/net/core/dev.c
> > > index 75bab5b0dbae..8e83b7099977 100644
> > > --- a/net/core/dev.c
> > > +++ b/net/core/dev.c
> > > @@ -3908,6 +3908,25 @@ sch_handle_egress(struct sk_buff *skb, int *ret, struct net_device *dev)
> > > 
> > >       return skb;
> > >   }
> > > +
> > > +static struct netdev_queue *
> > > +netdev_tx_queue_mapping(struct net_device *dev, struct sk_buff *skb)
> > > +{
> > > +     int qm = skb_get_queue_mapping(skb);
> > > +
> > > +     return netdev_get_tx_queue(dev, netdev_cap_txqueue(dev, qm));
> > > +}
> > > +
> > > +static bool netdev_xmit_txqueue_skipped(void)
> > > +{
> > > +     return __this_cpu_read(softnet_data.xmit.skip_txqueue);
> > > +}
> > > +
> > > +void netdev_xmit_skip_txqueue(bool skip)
> > > +{
> > > +     __this_cpu_write(softnet_data.xmit.skip_txqueue, skip);
> > > +}
> > > +EXPORT_SYMBOL_GPL(netdev_xmit_skip_txqueue);
> > >   #endif /* CONFIG_NET_EGRESS */
> > > 
> > >   #ifdef CONFIG_XPS
> > > @@ -4078,7 +4097,7 @@ struct netdev_queue *netdev_core_pick_tx(struct net_device *dev,
> > >   static int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
> > >   {
> > >       struct net_device *dev = skb->dev;
> > > -     struct netdev_queue *txq;
> > > +     struct netdev_queue *txq = NULL;
> > >       struct Qdisc *q;
> > >       int rc = -ENOMEM;
> > >       bool again = false;
> > > @@ -4106,11 +4125,17 @@ static int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
> > >                       if (!skb)
> > >                               goto out;
> > >               }
> > > +
> > > +             netdev_xmit_skip_txqueue(false);
> > > +
> > >               nf_skip_egress(skb, true);
> > >               skb = sch_handle_egress(skb, &rc, dev);
> > >               if (!skb)
> > >                       goto out;
> > >               nf_skip_egress(skb, false);
> > > +
> > > +             if (netdev_xmit_txqueue_skipped())
> > > +                     txq = netdev_tx_queue_mapping(dev, skb);
> > >       }
> > >   #endif
> > >       /* If device/qdisc don't need skb->dst, release it right now while
> > > @@ -4121,7 +4146,9 @@ static int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
> > >       else
> > >               skb_dst_force(skb);
> > > 
> > > -     txq = netdev_core_pick_tx(dev, skb, sb_dev);
> > > +     if (likely(!txq))
> > 
> > nit: Drop likely(). If the feature is used from sch_handle_egress(), then this would always be the case.
> Hi Daniel
> I think in most case, we don't use skbedit queue_mapping in the
> sch_handle_egress() , so I add likely in fast path.
> > > +             txq = netdev_core_pick_tx(dev, skb, sb_dev);
> > > +
> > >       q = rcu_dereference_bh(txq->qdisc);
> > 
> > How will the `netdev_xmit_skip_txqueue(true)` be usable from BPF side (see bpf_convert_ctx_access() ->
> > queue_mapping)?
> Good questions, In other patch, I introduce the
> bpf_netdev_skip_txqueue, so we can use netdev_xmit_skip_txqueue in bpf
> side

@Daniel: are you ok with the above explaination?

Thanks!

Paolo