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Date: Mon, 06 May 2024 14:51:35 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Abhishek Chauhan <quic_abchauha@...cinc.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
netdev@...r.kernel.org,
linux-kernel@...r.kernel.org,
Andrew Halaney <ahalaney@...hat.com>,
Willem de Bruijn <willemdebruijn.kernel@...il.com>,
Martin KaFai Lau <martin.lau@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Daniel Borkmann <daniel@...earbox.net>,
bpf <bpf@...r.kernel.org>
Cc: kernel@...cinc.com
Subject: Re: [RFC PATCH bpf-next v6 1/3] net: Rename mono_delivery_time to
tstamp_type for scalabilty
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@...cinc.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);
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