diff options
Diffstat (limited to 'sys/netinet/tcp_timer.h')
| -rw-r--r-- | sys/netinet/tcp_timer.h | 25 |
1 files changed, 21 insertions, 4 deletions
diff --git a/sys/netinet/tcp_timer.h b/sys/netinet/tcp_timer.h index 94c8a5e..e26a77c 100644 --- a/sys/netinet/tcp_timer.h +++ b/sys/netinet/tcp_timer.h @@ -92,11 +92,26 @@ /* * Minimum retransmit timer is 3 ticks, for algorithmic stability. - * The maximum is 64 seconds. The prior minimum of 1*hz (1 second) badly - * breaks throughput on any networks faster then a modem that has minor - * (e.g. 1%) packet loss. + * TCPT_RANGESET() will add another TCPTV_CPU_VAR to deal with + * the expected worst-case processing variances by the kernels + * representing the end points. Such variances do not always show + * up in the srtt because the timestamp is often calculated at + * the interface rather then at the TCP layer. This value is + * typically 50ms. However, it is also possible that delayed + * acks (typically 100ms) could create issues so we set the slop + * to 200ms to try to cover it. Note that, properly speaking, + * delayed-acks should not create a major issue for interactive + * environments which 'P'ush the last segment, at least as + * long as implementations do the required 'at least one ack + * for every two packets' for the non-interactive streaming case. + * (maybe the RTO calculation should use 2*RTT instead of RTT + * to handle the ack-every-other-packet case). + * + * The prior minimum of 1*hz (1 second) badly breaks throughput on any + * networks faster then a modem that has minor (e.g. 1%) packet loss. */ #define TCPTV_MIN ( 3 ) /* minimum allowable value */ +#define TCPTV_CPU_VAR ( hz/5 ) /* cpu variance allowed (200ms) */ #define TCPTV_REXMTMAX ( 64*hz) /* max allowable REXMT value */ #define TCPTV_TWTRUNC 8 /* RTO factor to truncate TW */ @@ -116,7 +131,7 @@ static char *tcptimers[] = * Force a time value to be in a certain range. */ #define TCPT_RANGESET(tv, value, tvmin, tvmax) do { \ - (tv) = (value); \ + (tv) = (value) + tcp_rexmit_slop; \ if ((u_long)(tv) < (u_long)(tvmin)) \ (tv) = (tvmin); \ else if ((u_long)(tv) > (u_long)(tvmax)) \ @@ -130,6 +145,8 @@ extern int tcp_keepintvl; /* time between keepalive probes */ extern int tcp_maxidle; /* time to drop after starting probes */ extern int tcp_delacktime; /* time before sending a delayed ACK */ extern int tcp_maxpersistidle; +extern int tcp_rexmit_min; +extern int tcp_rexmit_slop; extern int tcp_msl; extern int tcp_ttl; /* time to live for TCP segs */ extern int tcp_backoff[]; |
