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Makes Reno CC slightly loss tolerant #445

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Makes Reno CC slightly loss tolerant #445

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05e2148
Make reno CC a bit loss tolerant
janaiyengar Mar 22, 2021
af03c20
allow cwnd to increase if threshold has not yet been hit
janaiyengar Mar 22, 2021
c96cc14
comments cleanup
janaiyengar Mar 22, 2021
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4 changes: 4 additions & 0 deletions include/quicly/cc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,10 @@ typedef struct st_quicly_cc_t {
* Stash of acknowledged bytes, used during congestion avoidance.
*/
uint32_t stash;
/**
* Number of losses seen in a recovery episode.
*/
uint32_t num_lost_in_episode;
} reno;
/**
* State information for CUBIC congestion control.
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26 changes: 21 additions & 5 deletions lib/cc-reno.c
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Original file line number Diff line number Diff line change
Expand Up @@ -24,14 +24,17 @@

#define QUICLY_MIN_CWND 2
#define QUICLY_RENO_BETA 0.7
#define QUICLY_RENO_LOSS_THRESHOLD 2

/* TODO: Avoid increase if sender was application limited. */
static void reno_on_acked(quicly_cc_t *cc, const quicly_loss_t *loss, uint32_t bytes, uint64_t largest_acked, uint32_t inflight,
int64_t now, uint32_t max_udp_payload_size)
{
assert(inflight >= bytes);
/* Do not increase congestion window while in recovery. */
if (largest_acked < cc->recovery_end)
/* Do not increase congestion window while in recovery and if number of
* losses in this episode has met the threshold. */
if (largest_acked < cc->recovery_end &&
cc->state.reno.num_lost_in_episode >= QUICLY_RENO_LOSS_THRESHOLD)
return;

/* Slow start. */
Expand All @@ -56,10 +59,23 @@ static void reno_on_acked(quicly_cc_t *cc, const quicly_loss_t *loss, uint32_t b
static void reno_on_lost(quicly_cc_t *cc, const quicly_loss_t *loss, uint32_t bytes, uint64_t lost_pn, uint64_t next_pn,
int64_t now, uint32_t max_udp_payload_size)
{
/* Nothing to do if loss is in recovery window. */
if (lost_pn < cc->recovery_end)
/* Set up state if new recovery episode. */
if (lost_pn >= cc->recovery_end) {
cc->recovery_end = next_pn;
cc->state.reno.num_lost_in_episode = 0;
}

cc->state.reno.num_lost_in_episode++;

/* Nothing to do if number of losses in this recovery episode is below a
* threshold. Doing so builds some tolerance for loss, by only responding
* with a congestion action if the number of losses in a window is greater
* than the threshold. Similarly, there should be only one reduction in a
* window, so nothing to do if number of losses is greater than the
* threshold.
*/
if (cc->state.reno.num_lost_in_episode != QUICLY_RENO_LOSS_THRESHOLD)
return;
cc->recovery_end = next_pn;

++cc->num_loss_episodes;
if (cc->cwnd_exiting_slow_start == 0)
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