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tcp: add cwnd_undo functions to various tcp cc algorithms

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congestion control algorithms that do not halve cwnd in their .ssthresh
should provide a .cwnd_undo rather than rely on current fallback which
assumes reno halving (and thus doubles the cwnd).

All of these do 'something else' in their .ssthresh implementation, thus
store the cwnd on loss and provide .undo_cwnd to restore it again.

A followup patch will remove the fallback and all algorithms will
need to provide a .cwnd_undo function.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Florian Westphal
2016-11-21 14:18:37 +01:00
committed by David S. Miller
parent 2fcb58ab30
commit 85f7e7508a
5 changed files with 55 additions and 1 deletions
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10
net/ipv4/tcp_illinois.c
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@@ -48,6 +48,7 @@ struct illinois {
u32 end_seq; /* right edge of current RTT */
u32 alpha; /* Additive increase */
u32 beta; /* Muliplicative decrease */
u32 loss_cwnd; /* cwnd on loss */
u16 acked; /* # packets acked by current ACK */
u8 rtt_above; /* average rtt has gone above threshold */
u8 rtt_low; /* # of rtts measurements below threshold */
@@ -296,10 +297,18 @@ static u32 tcp_illinois_ssthresh(struct sock *sk)
struct tcp_sock *tp = tcp_sk(sk);
struct illinois *ca = inet_csk_ca(sk);
ca->loss_cwnd = tp->snd_cwnd;
/* Multiplicative decrease */
return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->beta) >> BETA_SHIFT), 2U);
}
static u32 tcp_illinois_cwnd_undo(struct sock *sk)
{
const struct illinois *ca = inet_csk_ca(sk);
return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
}
/* Extract info for Tcp socket info provided via netlink. */
static size_t tcp_illinois_info(struct sock *sk, u32 ext, int *attr,
union tcp_cc_info *info)
@@ -327,6 +336,7 @@ static size_t tcp_illinois_info(struct sock *sk, u32 ext, int *attr,
static struct tcp_congestion_ops tcp_illinois __read_mostly = {
.init = tcp_illinois_init,
.ssthresh = tcp_illinois_ssthresh,
.undo_cwnd = tcp_illinois_cwnd_undo,
.cong_avoid = tcp_illinois_cong_avoid,
.set_state = tcp_illinois_state,
.get_info = tcp_illinois_info,