| Message ID | 1326944879-22780-2-git-send-email-ncardwell@google.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Wed, 18 Jan 2012 22:47:59 -0500 Neal Cardwell <ncardwell@google.com> wrote: > 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> I was unsure of this, so forwarded it to the author and received his confirmation. Acked-by: Stephen Hemminger <shemminger@vyatta.com> Acked-by: Sangtae Ha <sangtae.ha@gmail.com> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Stephen Hemminger <shemminger@vyatta.com> Date: Thu, 19 Jan 2012 18:49:21 -0800 > On Wed, 18 Jan 2012 22:47:59 -0500 > Neal Cardwell <ncardwell@google.com> wrote: > >> 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> > > I was unsure of this, so forwarded it to the author > and received his confirmation. > > Acked-by: Stephen Hemminger <shemminger@vyatta.com> > Acked-by: Sangtae Ha <sangtae.ha@gmail.com> Applied. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index f376b05..a9077f4 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)
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> --- net/ipv4/tcp_cubic.c | 10 ++++++---- 1 files changed, 6 insertions(+), 4 deletions(-)