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Date: Mon, 06 May 2024 14:51:35 -0400
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Abhishek Chauhan <quic_abchauha@quicinc.com>, 
 "David S. Miller" <davem@davemloft.net>, 
 Eric Dumazet <edumazet@google.com>, 
 Jakub Kicinski <kuba@kernel.org>, 
 Paolo Abeni <pabeni@redhat.com>, 
 netdev@vger.kernel.org, 
 linux-kernel@vger.kernel.org, 
 Andrew Halaney <ahalaney@redhat.com>, 
 Willem de Bruijn <willemdebruijn.kernel@gmail.com>, 
 Martin KaFai Lau <martin.lau@kernel.org>, 
 Martin KaFai Lau <martin.lau@linux.dev>, 
 Daniel Borkmann <daniel@iogearbox.net>, 
 bpf <bpf@vger.kernel.org>
Cc: kernel@quicinc.com
Message-ID: <663926b74cbbd_516de29466@willemb.c.googlers.com.notmuch>
In-Reply-To: <20240504031331.2737365-2-quic_abchauha@quicinc.com>
References: <20240504031331.2737365-1-quic_abchauha@quicinc.com>
 <20240504031331.2737365-2-quic_abchauha@quicinc.com>
Subject: Re: [RFC PATCH bpf-next v6 1/3] net: Rename mono_delivery_time to
 tstamp_type for scalabilty
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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.
> 
> Also skb_set_delivery_type_by_clockid is a new function which accepts
> clockid to determine the tstamp_type.
> 
> 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@linux.dev/
> Signed-off-by: Abhishek Chauhan <quic_abchauha@quicinc.com>
> ---
> Changes since v5
> - Avoided using garble function names as mentioned by
>   Willem.
> - Implemented a conversion function stead of duplicating 
>   the same logic as mentioned by Willem.
> - Fixed indentation problems and minor documentation issues
>   which mentions tstamp_type as a whole instead of bitfield
>   notations. (Mentioned both by Willem and Martin)
>   
> Changes since v4
> - Introduce new function to directly delivery_time and
>   another to set tstamp_type based on clockid. 
> - Removed un-necessary comments in skbuff.h as 
>   enums were obvious and understood.
> 
> Changes since v3
> - Fixed inconsistent capitalization in skbuff.h
> - remove reference to MONO_DELIVERY_TIME_MASK in skbuff.h
>   and point it to skb_tstamp_type now.
> - Explicitely setting SKB_CLOCK_MONO if valid transmit_time
>   ip_send_unicast_reply 
> - Keeping skb_tstamp inline with skb_clear_tstamp. 
> - skb_set_delivery_time checks if timstamp is 0 and 
>   sets the tstamp_type to SKB_CLOCK_REAL.
> - Above comments are given by Willem 
> - Found out that skbuff.h has access to uapi/linux/time.h
>   So now instead of using  CLOCK_REAL/CLOCK_MONO 
>   i am checking actual clockid_t directly to set tstamp_type 
>   example:- CLOCK_REALTIME/CLOCK_MONOTONIC 
> - Compilation error fixed in 
>   net/ieee802154/6lowpan/reassembly.c
> 
> Changes since v2
> - Minor changes to commit subject
> 
> Changes since v1
> - Squashed the two commits into one as mentioned by Willem.
> - Introduced switch in skb_set_delivery_time.
> - Renamed and removed directionality aspects w.r.t tstamp_type 
>   as mentioned by Willem.
> 
>  include/linux/skbuff.h                     | 53 ++++++++++++++++------
>  include/net/inet_frag.h                    |  4 +-
>  net/bridge/netfilter/nf_conntrack_bridge.c |  6 +--
>  net/core/dev.c                             |  2 +-
>  net/core/filter.c                          | 10 ++--
>  net/ieee802154/6lowpan/reassembly.c        |  2 +-
>  net/ipv4/inet_fragment.c                   |  2 +-
>  net/ipv4/ip_fragment.c                     |  2 +-
>  net/ipv4/ip_output.c                       |  9 ++--
>  net/ipv4/tcp_output.c                      | 16 +++----
>  net/ipv6/ip6_output.c                      |  6 +--
>  net/ipv6/netfilter.c                       |  6 +--
>  net/ipv6/netfilter/nf_conntrack_reasm.c    |  2 +-
>  net/ipv6/reassembly.c                      |  2 +-
>  net/ipv6/tcp_ipv6.c                        |  2 +-
>  net/sched/act_bpf.c                        |  4 +-
>  net/sched/cls_bpf.c                        |  4 +-
>  17 files changed, 80 insertions(+), 52 deletions(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 1c2902eaebd3..de3915e2bfdb 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -706,6 +706,11 @@ typedef unsigned int sk_buff_data_t;
>  typedef unsigned char *sk_buff_data_t;
>  #endif
>  
> +enum skb_tstamp_type {
> +	SKB_CLOCK_REALTIME,
> +	SKB_CLOCK_MONOTONIC,
> +};
> +
>  /**
>   * DOC: Basic sk_buff geometry
>   *
> @@ -823,10 +828,9 @@ 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
> - *		delivery_time in mono clock base (i.e. EDT).  Otherwise, the
> - *		skb->tstamp has the (rcv) timestamp at ingress and
> - *		delivery_time at egress.
> + *	@tstamp_type: When set, skb->tstamp has the
> + *		delivery_time in mono clock base Otherwise, the
> + *		timestamp is considered real clock base.

Missing period. More importantly, no longer conditional. It always
captures the type of skb->tstamp.

> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -1301,7 +1301,7 @@ 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_type_by_clockid(skb, tp->tcp_wstamp_ns, CLOCK_MONOTONIC);
>  	if (clone_it) {
>  		oskb = skb;
>  
> @@ -1655,7 +1655,7 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
>  
>  	skb_split(skb, buff, len);
>  
> -	skb_set_delivery_time(buff, skb->tstamp, true);
> +	skb_set_delivery_type_by_clockid(buff, skb->tstamp, CLOCK_MONOTONIC);
>  	tcp_fragment_tstamp(skb, buff);

All these hardcoded monotonic calls in TCP can be the shorter version

    skb_set_delivery_type(.., SKB_CLOCK_MONOTONIC);