Re: [RFC PATCH bpf-next v4 1/2] net: Rename mono_delivery_time to tstamp_type for scalabilty

[Willem de Bruijn]

Abhishek Chauhan wrote:
> mono_delivery_time was added to check if skb->tstamp has delivery
> time in mono clock base (i.e. EDT) otherwise skb->tstamp has
> timestamp in ingress and delivery_time at egress.
> 
> Renaming the bitfield from mono_delivery_time to tstamp_type is for
> extensibilty for other timestamps such as userspace timestamp
> (i.e. SO_TXTIME) set via sock opts.
> 
> As we are renaming the mono_delivery_time to tstamp_type, it makes
> sense to start assigning tstamp_type based on enum defined
> in this commit.
> 
> Earlier we used bool arg flag to check if the tstamp is mono in
> function skb_set_delivery_time, Now the signature of the functions
> accepts tstamp_type to distinguish between mono and real time.
> 
> In future tstamp_type:1 can be extended to support userspace timestamp
> by increasing the bitfield.
> 
> Link: https://lore.kernel.org/netdev/bc037db4-58bb-4861-ac31-a361a93841d3@xxxxxxxxx/
> Signed-off-by: Abhishek Chauhan <quic_abchauha@xxxxxxxxxxx>

> +/**
> + * tstamp_type:1 can take 2 values each
> + * represented by time base in skb
> + * 0x0 => real timestamp_type
> + * 0x1 => mono timestamp_type
> + */
> +enum skb_tstamp_type {
> +	SKB_CLOCK_REAL,	/* Time base is skb is REALTIME */
> +	SKB_CLOCK_MONO,	/* Time base is skb is MONOTONIC */
> +};
> +

Can drop the comments. These names are self documenting.

>  /**
>   * DOC: Basic sk_buff geometry
>   *
> @@ -819,7 +830,7 @@ typedef unsigned char *sk_buff_data_t;
>   *	@dst_pending_confirm: need to confirm neighbour
>   *	@decrypted: Decrypted SKB
>   *	@slow_gro: state present at GRO time, slower prepare step required
> - *	@mono_delivery_time: When set, skb->tstamp has the
> + *	@tstamp_type: When set, skb->tstamp has the
>   *		delivery_time in mono clock base (i.e. EDT).  Otherwise, the
>   *		skb->tstamp has the (rcv) timestamp at ingress and
>   *		delivery_time at egress.

Is this still correct? I think all egress does now annotate correctly
as SKB_CLOCK_MONO. So when not set it always is SKB_CLOCK_REAL.

> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 61119d42b0fd..a062f88c47c3 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -1300,7 +1300,7 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
>  	tp = tcp_sk(sk);
>  	prior_wstamp = tp->tcp_wstamp_ns;
>  	tp->tcp_wstamp_ns = max(tp->tcp_wstamp_ns, tp->tcp_clock_cache);
> -	skb_set_delivery_time(skb, tp->tcp_wstamp_ns, true);
> +	skb_set_delivery_time(skb, tp->tcp_wstamp_ns, CLOCK_MONOTONIC);

Multiple references to CLOCK_MONOTONIC left