netdev - Re: [PATCH net-next v4 03/11] net-timestamp: reorganize in skb_tstamp_tx

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Message-ID: <6757009b87461_31657c294d6@willemb.c.googlers.com.notmuch>
Date: Mon, 09 Dec 2024 09:37:15 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Jason Xing <kerneljasonxing@...il.com>, 
 davem@...emloft.net, 
 edumazet@...gle.com, 
 kuba@...nel.org, 
 pabeni@...hat.com, 
 dsahern@...nel.org, 
 willemdebruijn.kernel@...il.com, 
 willemb@...gle.com, 
 ast@...nel.org, 
 daniel@...earbox.net, 
 andrii@...nel.org, 
 martin.lau@...ux.dev, 
 eddyz87@...il.com, 
 song@...nel.org, 
 yonghong.song@...ux.dev, 
 john.fastabend@...il.com, 
 kpsingh@...nel.org, 
 sdf@...ichev.me, 
 haoluo@...gle.com, 
 jolsa@...nel.org
Cc: bpf@...r.kernel.org, 
 netdev@...r.kernel.org, 
 Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v4 03/11] net-timestamp: reorganize in
 skb_tstamp_tx_output()

Jason Xing wrote:
> From: Jason Xing <kernelxing@...cent.com>
> 
> 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@...cent.com>
> ---
>  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.
>  
>  	/* 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
>