diff options
| author | Stephen Hemminger <shemminger@osdl.org> | 2007-04-08 23:45:04 +0200 |
|---|---|---|
| committer | Adrian Bunk <bunk@stusta.de> | 2007-04-08 23:45:04 +0200 |
| commit | 928fb605c9107cc5c4e4e77d99ea455651a4635f (patch) | |
| tree | 6cecc698ca017c7a8720ab894fa04f206bbdc935 | |
| parent | 289a332c20458518f27f4a32fe2a69364489c782 (diff) | |
| download | lwn-928fb605c9107cc5c4e4e77d99ea455651a4635f.tar.gz lwn-928fb605c9107cc5c4e4e77d99ea455651a4635f.zip | |
tcp: fix cubic scaling error
Doug Leith observed a discrepancy between the version of CUBIC described
in the papers and the version in 2.6.18. A math error related to scaling
causes Cubic to grow too slowly.
Patch is from "Sangtae Ha" <sha2@ncsu.edu>. I validated that
it does fix the problems.
See the following to show behavior over 500ms 100 Mbit link.
Sender (2.6.19-rc3) --- Bridge (2.6.18-rt7) ------- Receiver (2.6.19-rc3)
1G [netem] 100M
http://developer.osdl.org/shemminger/tcp/2.6.19-rc3/cubic-orig.png
http://developer.osdl.org/shemminger/tcp/2.6.19-rc3/cubic-fix.png
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
| -rw-r--r-- | net/ipv4/tcp_cubic.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index 31a4986dfbf7..4dae9a866806 100644 --- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -191,7 +191,7 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd) */ /* change the unit from HZ to bictcp_HZ */ - t = ((tcp_time_stamp + ca->delay_min - ca->epoch_start) + t = ((tcp_time_stamp + (ca->delay_min>>3) - ca->epoch_start) << BICTCP_HZ) / HZ; if (t < ca->bic_K) /* t - K */ @@ -260,7 +260,7 @@ static inline void measure_delay(struct sock *sk) (s32)(tcp_time_stamp - ca->epoch_start) < HZ) return; - delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr; + delay = (tcp_time_stamp - tp->rx_opt.rcv_tsecr)<<3; if (delay == 0) delay = 1; @@ -373,7 +373,7 @@ static int __init cubictcp_register(void) beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta); - cube_rtt_scale = (bic_scale << 3) / 10; /* 1024*c/rtt */ + cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */ /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3 * so K = cubic_root( (wmax-cwnd)*rtt/c ) |