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Fix for RTT calculation hang during congestion control.

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Only cache RTT on explicit stalls; Only use this cache for the
RTT decrease case. Otherwise use only local circuit RTT state for clock jump
checks.
This commit is contained in:
Mike Perry 2022-06-14 20:59:03 +00:00 committed by David Goulet
parent 254ca6717f
commit b0496d4019
1 changed files with 21 additions and 30 deletions
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51
src/core/or/congestion_control_common.c
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@ -695,10 +695,9 @@ congestion_control_update_circuit_estimates(congestion_control_t *cc,
static bool
time_delta_should_use_heuristics(const congestion_control_t *cc)
{
/* If we have exited slow start, we should have processed at least
* a cwnd worth of RTTs */
if (!cc->in_slow_start) {
/* If we have exited slow start and also have an EWMA RTT, we
* should have processed at least a cwnd worth of RTTs */
if (!cc->in_slow_start && cc->ewma_rtt_usec) {
return true;
}
@ -735,34 +734,27 @@ time_delta_stalled_or_jumped(const congestion_control_t *cc,
log_fn_ratelim(&stall_info_limit, LOG_INFO, LD_CIRC,
"Congestion control cannot measure RTT due to monotime stall.");
/* If delta is every 0, the monotime clock has stalled, and we should
* not use it anywhere. */
is_monotime_clock_broken = true;
return is_monotime_clock_broken;
}
/* If the old_delta is 0, we have no previous values on this circuit.
*
* So, return the global monotime status from other circuits, and
* do not update.
*/
if (old_delta == 0) {
return is_monotime_clock_broken;
return true;
}
/*
* For the heuristic cases, we need at least a few timestamps,
* to average out any previous partial stalls or jumps. So until
* than point, let's just use the cached status from other circuits.
* that point, let's just assume its OK.
*/
if (!time_delta_should_use_heuristics(cc)) {
return is_monotime_clock_broken;
return false;
}
/* If old_delta is significantly larger than new_delta, then
* this means that the monotime clock recently stopped moving
* forward. */
* this means that the monotime clock could have recently
* stopped moving forward. However, use the cache for this
* value, because it may also be caused by network activity,
* or by a previous clock jump that was not detected.
*
* So if we have not gotten a 0-delta recently, we will
* still allow this new low RTT, but just yell about it. */
if (old_delta > new_delta * DELTA_DISCREPENCY_RATIO_MAX) {
static ratelim_t dec_notice_limit = RATELIM_INIT(300);
log_fn_ratelim(&dec_notice_limit, LOG_NOTICE, LD_CIRC,
@ -770,29 +762,28 @@ time_delta_stalled_or_jumped(const congestion_control_t *cc,
"), likely due to clock jump.",
new_delta/1000, old_delta/1000);
is_monotime_clock_broken = true;
return is_monotime_clock_broken;
}
/* If new_delta is significantly larger than old_delta, then
* this means that the monotime clock suddenly jumped forward. */
* this means that the monotime clock suddenly jumped forward.
* However, do not cache this value, because it may also be caused
* by network activity.
*/
if (new_delta > old_delta * DELTA_DISCREPENCY_RATIO_MAX) {
static ratelim_t dec_notice_limit = RATELIM_INIT(300);
log_fn_ratelim(&dec_notice_limit, LOG_NOTICE, LD_CIRC,
log_fn_ratelim(&dec_notice_limit, LOG_PROTOCOL_WARN, LD_CIRC,
"Sudden increase in circuit RTT (%"PRIu64" vs %"PRIu64
"), likely due to clock jump.",
"), likely due to clock jump or suspended remote endpoint.",
new_delta/1000, old_delta/1000);
is_monotime_clock_broken = true;
return is_monotime_clock_broken;
return true;
}
/* All good! Update cached status, too */
is_monotime_clock_broken = false;
return is_monotime_clock_broken;
return false;
}
/**