Merge branch 'tcp-TCP-TS-option-use-1-ms-clock'
Eric Dumazet says:
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tcp: TCP TS option use 1 ms clock
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
====================
Signed-off-by: David S. Miller <davem@davemloft.net>