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authorNeal Cardwell <ncardwell@google.com>2012-01-18 17:47:59 +0000
committerDavid S. Miller <davem@davemloft.net>2012-01-20 14:17:26 -0500
commit5a45f0086a2dcf50db7e6a0bf5be933880f85127 (patch)
treef67d6ddb68c276bcf34077e7442b0ca722144c75 /net
parentfc16dcd8c2e1e9bc91ed765957e1f2bbf334253e (diff)
downloadlinux-linaro-stable-5a45f0086a2dcf50db7e6a0bf5be933880f85127.tar.gz
tcp: fix undo after RTO for CUBIC
This patch fixes CUBIC so that cwnd reductions made during RTOs can be undone (just as they already can be undone when using the default/Reno behavior). When undoing cwnd reductions, BIC-derived congestion control modules were restoring the cwnd from last_max_cwnd. There were two problems with using last_max_cwnd to restore a cwnd during undo: (a) last_max_cwnd was set to 0 on state transitions into TCP_CA_Loss (by calling the module's reset() functions), so cwnd reductions from RTOs could not be undone. (b) when fast_covergence is enabled (which it is by default) last_max_cwnd does not actually hold the value of snd_cwnd before the loss; instead, it holds a scaled-down version of snd_cwnd. This patch makes the following changes: (1) upon undo, revert snd_cwnd to ca->loss_cwnd, which is already, as the existing comment notes, the "congestion window at last loss" (2) stop forgetting ca->loss_cwnd on TCP_CA_Loss events (3) use ca->last_max_cwnd to check if we're in slow start Signed-off-by: Neal Cardwell <ncardwell@google.com> Acked-by: Stephen Hemminger <shemminger@vyatta.com> Acked-by: Sangtae Ha <sangtae.ha@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/ipv4/tcp_cubic.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index f376b05cca81..a9077f441cb2 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -107,7 +107,6 @@ static inline void bictcp_reset(struct bictcp *ca)
{
ca->cnt = 0;
ca->last_max_cwnd = 0;
- ca->loss_cwnd = 0;
ca->last_cwnd = 0;
ca->last_time = 0;
ca->bic_origin_point = 0;
@@ -142,7 +141,10 @@ static inline void bictcp_hystart_reset(struct sock *sk)
static void bictcp_init(struct sock *sk)
{
- bictcp_reset(inet_csk_ca(sk));
+ struct bictcp *ca = inet_csk_ca(sk);
+
+ bictcp_reset(ca);
+ ca->loss_cwnd = 0;
if (hystart)
bictcp_hystart_reset(sk);
@@ -275,7 +277,7 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
* The initial growth of cubic function may be too conservative
* when the available bandwidth is still unknown.
*/
- if (ca->loss_cwnd == 0 && ca->cnt > 20)
+ if (ca->last_max_cwnd == 0 && ca->cnt > 20)
ca->cnt = 20; /* increase cwnd 5% per RTT */
/* TCP Friendly */
@@ -342,7 +344,7 @@ static u32 bictcp_undo_cwnd(struct sock *sk)
{
struct bictcp *ca = inet_csk_ca(sk);
- return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd);
+ return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
}
static void bictcp_state(struct sock *sk, u8 new_state)