ChangeSet 1.1537.1.43, 2005/02/21 17:54:02-08:00, [EMAIL PROTECTED]
[TCP]: Fix BIC max_cwnd calculation error.
The BIC TCP cwnd problem as identified by Yee-Ting Li and Doug Leith
is that the computation is recalc_ssthresh is incorrect and
BICTCP_1_OVER_BETA/2 should be BICTCP_1_OVER_BETA*2.
My fix is to implement the code from BIC TCP 1.1 which uses a sysctl
to set the beta. There are a few variable name changes from the 1.1
code, and made the scaling factor a #define instead of hardcoded.
I validated this using netem and kprobes, for more details see
http://developer.osdl.org/shemminger/bic-beta-patch.pdf
Signed-off-by: Stephen Hemminger <[EMAIL PROTECTED]>
Signed-off-by: David S. Miller <[EMAIL PROTECTED]>
include/linux/sysctl.h | 1 +
include/net/tcp.h | 17 +++++++++--------
net/ipv4/sysctl_net_ipv4.c | 3 +++
net/ipv4/tcp_input.c | 1 +
4 files changed, 14 insertions(+), 8 deletions(-)
diff -Nru a/include/linux/sysctl.h b/include/linux/sysctl.h
--- a/include/linux/sysctl.h 2005-02-23 10:06:39 -08:00
+++ b/include/linux/sysctl.h 2005-02-23 10:06:39 -08:00
@@ -326,6 +326,7 @@
NET_TCP_BIC_LOW_WINDOW=104,
NET_TCP_DEFAULT_WIN_SCALE=105,
NET_TCP_MODERATE_RCVBUF=106,
+ NET_TCP_BIC_BETA=108,
};
enum {
diff -Nru a/include/net/tcp.h b/include/net/tcp.h
--- a/include/net/tcp.h 2005-02-23 10:06:39 -08:00
+++ b/include/net/tcp.h 2005-02-23 10:06:39 -08:00
@@ -395,9 +395,8 @@
# define TCP_TW_RECYCLE_TICK (12+2-TCP_TW_RECYCLE_SLOTS_LOG)
#endif
-#define BICTCP_1_OVER_BETA 8 /*
- * Fast recovery
- * multiplicative decrease factor
+#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
+ * max_cwnd = snd_cwnd * beta
*/
#define BICTCP_MAX_INCREMENT 32 /*
* Limit on the amount of
@@ -491,6 +490,7 @@
extern int sysctl_tcp_bic;
extern int sysctl_tcp_bic_fast_convergence;
extern int sysctl_tcp_bic_low_window;
+extern int sysctl_tcp_bic_beta;
extern int sysctl_tcp_default_win_scale;
extern int sysctl_tcp_moderate_rcvbuf;
@@ -1132,15 +1132,16 @@
if (tcp_is_bic(tp)) {
if (sysctl_tcp_bic_fast_convergence &&
tp->snd_cwnd < tp->bictcp.last_max_cwnd)
- tp->bictcp.last_max_cwnd
- = (tp->snd_cwnd * (2*BICTCP_1_OVER_BETA-1))
- / (BICTCP_1_OVER_BETA/2);
+ tp->bictcp.last_max_cwnd = (tp->snd_cwnd *
+ (BICTCP_BETA_SCALE
+ + sysctl_tcp_bic_beta))
+ / (2 * BICTCP_BETA_SCALE);
else
tp->bictcp.last_max_cwnd = tp->snd_cwnd;
if (tp->snd_cwnd > sysctl_tcp_bic_low_window)
- return max(tp->snd_cwnd -
(tp->snd_cwnd/BICTCP_1_OVER_BETA),
- 2U);
+ return max((tp->snd_cwnd * sysctl_tcp_bic_beta)
+ / BICTCP_BETA_SCALE, 2U);
}
return max(tp->snd_cwnd >> 1U, 2U);
diff -Nru a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
--- a/net/ipv4/sysctl_net_ipv4.c 2005-02-23 10:06:39 -08:00
+++ b/net/ipv4/sysctl_net_ipv4.c 2005-02-23 10:06:39 -08:00
@@ -268,6 +268,9 @@
{NET_TCP_MODERATE_RCVBUF, "tcp_moderate_rcvbuf",
&sysctl_tcp_moderate_rcvbuf, sizeof(int), 0644, NULL,
&proc_dointvec},
+ {NET_TCP_BIC_BETA, "tcp_bic_beta",
+ &sysctl_tcp_bic_beta, sizeof(int), 0644, NULL,
+ &proc_dointvec},
{0}
};
diff -Nru a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
--- a/net/ipv4/tcp_input.c 2005-02-23 10:06:39 -08:00
+++ b/net/ipv4/tcp_input.c 2005-02-23 10:06:39 -08:00
@@ -107,6 +107,7 @@
int sysctl_tcp_bic;
int sysctl_tcp_bic_fast_convergence = 1;
int sysctl_tcp_bic_low_window = 14;
+int sysctl_tcp_bic_beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
#define FLAG_DATA 0x01 /* Incoming frame contained data.
*/
#define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window
update. */
-
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