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| author | Eric Dumazet <edumazet@google.com> | 2015-08-21 17:38:02 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2015-08-25 11:33:54 -0700 |
| commit | 43e122b014c955a33220fabbd09c4b5e4f422c3c (patch) | |
| tree | a5accf2276666812aed04749e3b6f44505a5cbab /Documentation | |
| parent | 4ec3b28c2763e11a423d03810ff0be65f02e635e (diff) | |
| download | lwn-43e122b014c955a33220fabbd09c4b5e4f422c3c.tar.gz lwn-43e122b014c955a33220fabbd09c4b5e4f422c3c.zip | |
tcp: refine pacing rate determination
When TCP pacing was added back in linux-3.12, we chose
to apply a fixed ratio of 200 % against current rate,
to allow probing for optimal throughput even during
slow start phase, where cwnd can be doubled every other gRTT.
At Google, we found it was better applying a different ratio
while in Congestion Avoidance phase.
This ratio was set to 120 %.
We've used the normal tcp_in_slow_start() helper for a while,
then tuned the condition to select the conservative ratio
as soon as cwnd >= ssthresh/2 :
- After cwnd reduction, it is safer to ramp up more slowly,
as we approach optimal cwnd.
- Initial ramp up (ssthresh == INFINITY) still allows doubling
cwnd every other RTT.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/networking/ip-sysctl.txt | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt index 46e88ed7f41d..ac77a13d2ea2 100644 --- a/Documentation/networking/ip-sysctl.txt +++ b/Documentation/networking/ip-sysctl.txt @@ -586,6 +586,21 @@ tcp_min_tso_segs - INTEGER if available window is too small. Default: 2 +tcp_pacing_ss_ratio - INTEGER + sk->sk_pacing_rate is set by TCP stack using a ratio applied + to current rate. (current_rate = cwnd * mss / srtt) + If TCP is in slow start, tcp_pacing_ss_ratio is applied + to let TCP probe for bigger speeds, assuming cwnd can be + doubled every other RTT. + Default: 200 + +tcp_pacing_ca_ratio - INTEGER + sk->sk_pacing_rate is set by TCP stack using a ratio applied + to current rate. (current_rate = cwnd * mss / srtt) + If TCP is in congestion avoidance phase, tcp_pacing_ca_ratio + is applied to conservatively probe for bigger throughput. + Default: 120 + tcp_tso_win_divisor - INTEGER This allows control over what percentage of the congestion window can be consumed by a single TSO frame. |