Re: [PATCH net-next v4 03/11] net-timestamp: reorganize in skb_tstamp_tx_output()

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On Mon, Dec 9, 2024 at 10:37 PM Willem de Bruijn
<willemdebruijn.kernel@xxxxxxxxx> wrote:
>
> Jason Xing wrote:
> > From: Jason Xing <kernelxing@xxxxxxxxxxx>
> >
> > It's a prep for bpf print function later. This patch only puts the
> > original generating logic into one function, so that we integrate
> > bpf print easily. No functional changes here.
> >
> > Signed-off-by: Jason Xing <kernelxing@xxxxxxxxxxx>
> > ---
> >  include/linux/skbuff.h |  4 ++--
> >  net/core/dev.c         |  3 +--
> >  net/core/skbuff.c      | 41 +++++++++++++++++++++++++++++++++++------
> >  3 files changed, 38 insertions(+), 10 deletions(-)
> >
> > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> > index 58009fa66102..53c6913560e4 100644
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -39,6 +39,7 @@
> >  #include <net/net_debug.h>
> >  #include <net/dropreason-core.h>
> >  #include <net/netmem.h>
> > +#include <uapi/linux/errqueue.h>
> >
> >  /**
> >   * DOC: skb checksums
> > @@ -4535,8 +4536,7 @@ void skb_tstamp_tx(struct sk_buff *orig_skb,
> >  static inline void skb_tx_timestamp(struct sk_buff *skb)
> >  {
> >       skb_clone_tx_timestamp(skb);
> > -     if (skb_shinfo(skb)->tx_flags & SKBTX_SW_TSTAMP)
> > -             skb_tstamp_tx(skb, NULL);
> > +     __skb_tstamp_tx(skb, NULL, NULL, skb->sk, SCM_TSTAMP_SND);
> >  }
> >
> >  /**
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index 45a8c3dd4a64..5d584950564b 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -4350,8 +4350,7 @@ int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
> >       skb_reset_mac_header(skb);
> >       skb_assert_len(skb);
> >
> > -     if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_SCHED_TSTAMP))
> > -             __skb_tstamp_tx(skb, NULL, NULL, skb->sk, SCM_TSTAMP_SCHED);
> > +     __skb_tstamp_tx(skb, NULL, NULL, skb->sk, SCM_TSTAMP_SCHED);
>
> This adds a function call in the hot path, as __skb_tstamp_tx is
> defined in a .c file.
>
> Currently this is only well predicted branch on a likely cache hot
> variable.

Oh, right, thanks for reminding me. I will figure out a better solution :)

> >
> >       /* Disable soft irqs for various locks below. Also
> >        * stops preemption for RCU.
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index 6841e61a6bd0..74b840ffaf94 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -5539,10 +5539,10 @@ void skb_complete_tx_timestamp(struct sk_buff *skb,
> >  }
> >  EXPORT_SYMBOL_GPL(skb_complete_tx_timestamp);
> >
> > -void __skb_tstamp_tx(struct sk_buff *orig_skb,
> > -                  const struct sk_buff *ack_skb,
> > -                  struct skb_shared_hwtstamps *hwtstamps,
> > -                  struct sock *sk, int tstype)
> > +static void skb_tstamp_tx_output(struct sk_buff *orig_skb,
> > +                              const struct sk_buff *ack_skb,
> > +                              struct skb_shared_hwtstamps *hwtstamps,
> > +                              struct sock *sk, int tstype)
> >  {
> >       struct sk_buff *skb;
> >       bool tsonly, opt_stats = false;
> > @@ -5594,13 +5594,42 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb,
> >
> >       __skb_complete_tx_timestamp(skb, sk, tstype, opt_stats);
> >  }
> > +
> > +static bool skb_tstamp_is_set(const struct sk_buff *skb, int tstype)
> > +{
> > +     switch (tstype) {
> > +     case SCM_TSTAMP_SCHED:
> > +             if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_SCHED_TSTAMP))
> > +                     return true;
> > +             return false;
> > +     case SCM_TSTAMP_SND:
> > +             if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_SW_TSTAMP))
> > +                     return true;
>
> Also true for SKBTX_HW_TSTAMP
>
> > +             return false;
> > +     case SCM_TSTAMP_ACK:
> > +             if (TCP_SKB_CB(skb)->txstamp_ack)
> > +                     return true;
> > +             return false;
> > +     }
> > +
> > +     return false;
> > +}
> > +
> > +void __skb_tstamp_tx(struct sk_buff *orig_skb,
> > +                  const struct sk_buff *ack_skb,
> > +                  struct skb_shared_hwtstamps *hwtstamps,
> > +                  struct sock *sk, int tstype)
> > +{
> > +     if (unlikely(skb_tstamp_is_set(orig_skb, tstype)))
> > +             skb_tstamp_tx_output(orig_skb, ack_skb, hwtstamps, sk, tstype);
> > +}
> >  EXPORT_SYMBOL_GPL(__skb_tstamp_tx);
> >
> >  void skb_tstamp_tx(struct sk_buff *orig_skb,
> >                  struct skb_shared_hwtstamps *hwtstamps)
> >  {
> > -     return __skb_tstamp_tx(orig_skb, NULL, hwtstamps, orig_skb->sk,
> > -                            SCM_TSTAMP_SND);
> > +     return skb_tstamp_tx_output(orig_skb, NULL, hwtstamps, orig_skb->sk,
> > +                                 SCM_TSTAMP_SND);
> >  }
> >  EXPORT_SYMBOL_GPL(skb_tstamp_tx);
> >
> > --
> > 2.37.3
> >
>
>





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