TCP Timestamps option is defined in RFC 7323 Traditionally on linux, it has been tied to the internal 'jiffy' variable, because it had been a cheap and good enough generator.
Unfortunately some distros use HZ=250 or even HZ=100 leading to not very useful TCP timestamps. For TCP flows in the DC, Google has used usec resolution for more than two years with great success [1]. RCVBUF autotuning is more precise. This series converts tp->tcp_mstamp to a plain u64 value storing a 1 usec TCP clock. This choice will allow us to upstream the 1 usec TS option as discussed in IETF 97. Kathleen Nichols [2] and others advocate for 1ms TS clocks for network analysis. (1ms being the lowest value supported by RFC 7323.) [1] https://www.ietf.org/proceedings/97/slides/slides-97-tcpm-tcp-options-for-low-latency-00.pdf [2] http://netseminar.stanford.edu/seminars/02_02_17.pdf Eric Dumazet (15): tcp: use tp->tcp_mstamp in output path tcp: introduce tcp_jiffies32 dccp: do not use tcp_time_stamp tcp: use tcp_jiffies32 to feed tp->lsndtime tcp: use tcp_jiffies32 to feed tp->snd_cwnd_stamp tcp_bbr: use tcp_jiffies32 instead of tcp_time_stamp tcp: bic,cubic: use tcp_jiffies32 instead of tcp_time_stamp tcp: use tcp_jiffies32 for rcv_tstamp and lrcvtime tcp: use tcp_jiffies32 to feed probe_timestamp tcp: uses jiffies_32 to feed tp->chrono_start tcp: use tcp_jiffies32 in __tcp_oow_rate_limited() tcp_westwood: use tcp_jiffies32 instead of tcp_time_stamp tcp_lp: cache tcp_time_stamp tcp: replace misc tcp_time_stamp to tcp_jiffies32 tcp: switch TCP TS option (RFC 7323) to 1ms clock include/linux/skbuff.h | 62 +------------------ include/linux/tcp.h | 22 +++---- include/net/tcp.h | 74 ++++++++++++++++++----- net/dccp/ccids/ccid2.c | 8 +-- net/dccp/ccids/ccid2.h | 2 +- net/ipv4/syncookies.c | 8 +-- net/ipv4/tcp.c | 10 ++-- net/ipv4/tcp_bbr.c | 34 +++++------ net/ipv4/tcp_bic.c | 6 +- net/ipv4/tcp_cubic.c | 14 ++--- net/ipv4/tcp_htcp.c | 2 +- net/ipv4/tcp_input.c | 126 +++++++++++++++++++-------------------- net/ipv4/tcp_ipv4.c | 16 ++--- net/ipv4/tcp_lp.c | 17 +++--- net/ipv4/tcp_metrics.c | 2 +- net/ipv4/tcp_minisocks.c | 8 +-- net/ipv4/tcp_output.c | 51 ++++++++-------- net/ipv4/tcp_rate.c | 16 ++--- net/ipv4/tcp_recovery.c | 24 ++++---- net/ipv4/tcp_timer.c | 17 +++--- net/ipv4/tcp_westwood.c | 6 +- net/ipv6/syncookies.c | 2 +- net/ipv6/tcp_ipv6.c | 4 +- net/netfilter/nf_synproxy_core.c | 2 +- 24 files changed, 259 insertions(+), 274 deletions(-) -- 2.13.0.303.g4ebf302169-goog
