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Factor out timing ack and drop code.

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david
2011-12-31 21:59:57 +00:00
parent 8d52190d9d
commit 8ba1cf6b15
4 changed files with 77 additions and 122 deletions
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58
timing.cc
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@@ -229,6 +229,64 @@ void enforce_scan_delay(struct timeval *tv) {
return;
}
/* Returns the scaling factor to use when incrementing the congestion
window. */
double ultra_timing_vals::cc_scale(const struct scan_performance_vars *perf) {
double ratio;
assert(num_replies_received > 0);
ratio = (double) num_replies_expected / num_replies_received;
return MIN(ratio, perf->cc_scale_max);
}
/* Update congestion variables for the receipt of a reply. */
void ultra_timing_vals::ack(const struct scan_performance_vars *perf, double scale) {
num_replies_received++;
if (cwnd < ssthresh) {
/* In slow start mode. "During slow start, a TCP increments cwnd by at most
SMSS bytes for each ACK received that acknowledges new data." */
cwnd += perf->slow_incr * cc_scale(perf) * scale;
if (cwnd > ssthresh)
cwnd = ssthresh;
} else {
/* Congestion avoidance mode. "During congestion avoidance, cwnd is
incremented by 1 full-sized segment per round-trip time (RTT). The
equation
cwnd += SMSS*SMSS/cwnd
provides an acceptable approximation to the underlying principle of
increasing cwnd by 1 full-sized segment per RTT." */
cwnd += perf->ca_incr / cwnd * cc_scale(perf) * scale;
}
if (cwnd > perf->max_cwnd)
cwnd = perf->max_cwnd;
}
/* Update congestion variables for a detected drop. */
void ultra_timing_vals::drop(unsigned in_flight,
const struct scan_performance_vars *perf, const struct timeval *now) {
/* "When a TCP sender detects segment loss using the retransmission timer, the
value of ssthresh MUST be set to no more than the value
ssthresh = max (FlightSize / 2, 2*SMSS)
Furthermore, upon a timeout cwnd MUST be set to no more than the loss
window, LW, which equals 1 full-sized segment (regardless of the value of
IW)." */
cwnd = perf->low_cwnd;
ssthresh = (int) MAX(in_flight / perf->host_drop_ssthresh_divisor, 2);
last_drop = *now;
}
/* Update congestion variables for a detected drop, but less aggressively for
group congestion control. */
void ultra_timing_vals::drop_group(unsigned in_flight,
const struct scan_performance_vars *perf, const struct timeval *now) {
cwnd = MAX(perf->low_cwnd, cwnd / perf->group_drop_cwnd_divisor);
ssthresh = (int) MAX(in_flight / perf->group_drop_ssthresh_divisor, 2);
last_drop = *now;
}
/* Do initialization after the global NmapOps table has been filled in. */
void scan_performance_vars::init() {
/* TODO: I should revisit these values for tuning. They should probably