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authorEric Dumazet <edumazet@google.com>2015-08-21 17:38:02 -0700
committerDavid S. Miller <davem@davemloft.net>2015-08-25 11:33:54 -0700
commit43e122b014c955a33220fabbd09c4b5e4f422c3c (patch)
treea5accf2276666812aed04749e3b6f44505a5cbab /Documentation/networking
parent4ec3b28c2763e11a423d03810ff0be65f02e635e (diff)
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/networking')
-rw-r--r--Documentation/networking/ip-sysctl.txt15
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.