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Guard against 0 time delta in BDP calc.

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This can only happen in Shadow, but it will cause issues there.
This commit is contained in:
Mike Perry
2022-01-21 18:40:49 +00:00
parent 8052d0c2c0
commit 4f3a0e39cf
1 changed files with 18 additions and 13 deletions
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src/core/or/congestion_control_common.c
+18 -13
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@@ -937,21 +937,26 @@ congestion_control_update_circuit_bdp(congestion_control_t *cc,
timestamp_usec = peek_timestamp(cc->sendme_arrival_timestamps);
uint64_t delta = now_usec - timestamp_usec;
/* The acked data is in sendme_cnt-1 chunks, because we are counting the
* data that is processed by the other endpoint *between* all of these
* sendmes. There's one less gap between the sendmes than the number
* of sendmes. */
uint64_t cells = (sendme_cnt-1)*cc->sendme_inc;
/* In Shadow, the time delta between acks can be 0 if there is no
* network activity between them. Only update BDP if the delta is
* non-zero. */
if (delta > 0) {
/* The acked data is in sendme_cnt-1 chunks, because we are counting
* the data that is processed by the other endpoint *between* all of
* these sendmes. There's one less gap between the sendmes than the
* number of sendmes. */
uint64_t cells = (sendme_cnt-1)*cc->sendme_inc;
/* The bandwidth estimate is cells/delta, which when multiplied
* by min RTT obtains the BDP. However, we multiply first to
* avoid precision issues with the RTT being close to delta in size. */
sendme_rate_bdp = cells*cc->min_rtt_usec/delta;
/* The bandwidth estimate is cells/delta, which when multiplied
* by min RTT obtains the BDP. However, we multiply first to
* avoid precision issues with the RTT being close to delta in size. */
sendme_rate_bdp = cells*cc->min_rtt_usec/delta;
/* Calculate BDP_EWMA_COUNT N-EWMA */
cc->bdp[BDP_ALG_SENDME_RATE] =
n_count_ewma(sendme_rate_bdp, cc->bdp[BDP_ALG_SENDME_RATE],
cc->ewma_cwnd_cnt*sendme_acks_per_cwnd(cc));
/* Calculate BDP_EWMA_COUNT N-EWMA */
cc->bdp[BDP_ALG_SENDME_RATE] =
n_count_ewma(sendme_rate_bdp, cc->bdp[BDP_ALG_SENDME_RATE],
cc->ewma_cwnd_cnt*sendme_acks_per_cwnd(cc));
}
}
/* In-flight BDP will cause the cwnd to drift down when underutilized.