netdev - Re: [PATCH net-next 00/13] tcp: add optional usec resolution to TCP TS

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Message-ID: <CAK6E8=dZHwS3ULq2zxyBNcnff8z=8E+1W=SYQdOm8qjn5cQTAg@mail.gmail.com>
Date: Fri, 20 Oct 2023 09:10:46 -0700
From: Yuchung Cheng <ycheng@...gle.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, 
	Neal Cardwell <ncardwell@...gle.com>, Kevin Yang <yyd@...gle.com>, 
	Soheil Hassas Yeganeh <soheil@...gle.com>, Wei Wang <weiwan@...gle.com>, Van Jacobson <vanj@...gle.com>, 
	Florian Westphal <fw@...len.de>, eric.dumazet@...il.com
Subject: Re: [PATCH net-next 00/13] tcp: add optional usec resolution to TCP TS

On Fri, Oct 20, 2023 at 5:57 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> As discussed in various public places in 2016, Google adopted
> usec resolution in RFC 7323 TS values, at Van Jacobson suggestion.
>
> Goals were :
>
> 1) better observability of delays in networking stacks/fabrics.
>
> 2) better disambiguation of events based on TSval/ecr values.
>
> 3) building block for congestion control modules needing usec resolution.
>
> Back then we implemented a schem based on private SYN options
> to safely negotiate the feature.
>
> For upstream submission, we chose to use a much simpler route
> attribute because this feature is probably going to be used
> in private networks.
>
> ip route add 10/8 ... features tcp_usec_ts
>
> References:
>
> https://www.ietf.org/proceedings/97/slides/slides-97-tcpm-tcp-options-for-low-latency-00.pdf
> https://datatracker.ietf.org/doc/draft-wang-tcpm-low-latency-opt/
>
> First two patches are fixing old minor bugs and might be taken
> by stable teams (thanks to appropriate Fixes: tags)

Huge thanks to Eric for making this happen for real :-) an immediate
benefit is enabling TCP timestamp based undos (Eifel) for short RTT
transactions. This allows datacenter TCP to use more aggressive
timeout w/o worrying too much of spurious timeout cwnd effect

Acked-by: Yuchung Cheng <ycheng@...gle.com>


>
> Eric Dumazet (13):
>   chtls: fix tp->rcv_tstamp initialization
>   tcp: fix cookie_init_timestamp() overflows
>   tcp: add tcp_time_stamp_ms() helper
>   tcp: introduce tcp_clock_ms()
>   tcp: replace tcp_time_stamp_raw()
>   tcp: rename tcp_skb_timestamp()
>   tcp: move tcp_ns_to_ts() to net/ipv4/syncookies.c
>   tcp: rename tcp_time_stamp() to tcp_time_stamp_ts()
>   tcp: add tcp_rtt_tsopt_us()
>   tcp: add RTAX_FEATURE_TCP_USEC_TS
>   tcp: introduce TCP_PAWS_WRAP
>   tcp: add support for usec resolution in TCP TS values
>   tcp: add TCPI_OPT_USEC_TS
>
>  .../chelsio/inline_crypto/chtls/chtls_cm.c    |  2 +-
>  include/linux/tcp.h                           |  9 ++-
>  include/net/inet_timewait_sock.h              |  3 +-
>  include/net/tcp.h                             | 59 ++++++++++++++-----
>  include/uapi/linux/rtnetlink.h                | 18 +++---
>  include/uapi/linux/tcp.h                      |  1 +
>  net/ipv4/syncookies.c                         | 32 ++++++----
>  net/ipv4/tcp.c                                | 26 +++++---
>  net/ipv4/tcp_input.c                          | 52 ++++++++--------
>  net/ipv4/tcp_ipv4.c                           |  5 +-
>  net/ipv4/tcp_lp.c                             |  2 +-
>  net/ipv4/tcp_minisocks.c                      | 19 ++++--
>  net/ipv4/tcp_output.c                         | 14 +++--
>  net/ipv4/tcp_timer.c                          | 44 +++++++++-----
>  net/ipv6/tcp_ipv6.c                           |  5 +-
>  net/netfilter/nf_synproxy_core.c              |  2 +-
>  .../selftests/bpf/progs/xdp_synproxy_kern.c   |  4 +-
>  17 files changed, 193 insertions(+), 104 deletions(-)
>
> --
> 2.42.0.655.g421f12c284-goog
>