tcp_cubic: switch bictcp_clock() to usec resolution

Browse source

Current 1ms clock feeds ca->round_start, ca->delay_min,
ca->last_ack.

This is quite problematic for data-center flows, where delay_min
is way below 1 ms.

This means Hystart Train detection triggers every time jiffies value
is updated, since "((s32)(now - ca->round_start) > ca->delay_min >> 4)"
expression becomes true.

This kind of random behavior can be solved by reusing the existing
usec timestamp that TCP keeps in tp->tcp_mstamp

Note that a followup patch will tweak things a bit, because
during slow start, GRO aggregation on receivers naturally
increases the RTT as TSO packets gradually come to ~64KB size.

To recap, right after this patch CUBIC Hystart train detection
is more aggressive, since short RTT flows might exit slow start at
cwnd = 20, instead of being possibly unbounded.

Following patch will address this problem.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

...

This commit is contained in:

Eric Dumazet 2019-12-23 12:27:52 -08:00 • committed by David S. Miller

parent 35821fc2b4

commit cff04e2da3

1 changed files with 14 additions and 21 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

35

net/ipv4/tcp_cubic.c

View file