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tcp: do not slow start when cwnd equals ssthresh

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In the original design slow start is only used to raise cwnd
when cwnd is stricly below ssthresh. It makes little sense
to slow start when cwnd == ssthresh: especially
when hystart has set ssthresh in the initial ramp, or after
recovery when cwnd resets to ssthresh. Not doing so will
also help reduce the buffer bloat slightly.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Nandita Dukkipati <nanditad@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Yuchung Cheng
2015-07-09 13:16:30 -07:00
committed by David S. Miller
parent 071d5080e3
commit 76174004a0
4 changed files with 4 additions and 6 deletions
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4
net/ipv4/tcp_cong.c
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@@ -365,10 +365,8 @@ int tcp_set_congestion_control(struct sock *sk, const char *name)
*/
u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
{
u32 cwnd = tp->snd_cwnd + acked;
u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
if (cwnd > tp->snd_ssthresh)
cwnd = tp->snd_ssthresh + 1;
acked -= cwnd - tp->snd_cwnd;
tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);