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authorDimitri Staessens <dimitri.staessens@ugent.be>2019-02-08 10:47:42 +0100
committerSander Vrijders <sander.vrijders@ugent.be>2019-02-08 12:39:23 +0100
commite00c9b13acad23e14df9d5cf4c7868dfd6e1bc55 (patch)
tree1447e0402a78b79edd03cd8f72bc6c236df81a4c /src/lib/rxmwheel.c
parent5dd086aa679e3e05d20ef6a19f3fefbe46ffe40e (diff)
downloadouroboros-e00c9b13acad23e14df9d5cf4c7868dfd6e1bc55.tar.gz
ouroboros-e00c9b13acad23e14df9d5cf4c7868dfd6e1bc55.zip
lib: Add initial rtt estimator to FRCT
This adds a simple round-trip time estimator to FRCT. The estimate is a weighted average with deviation. The retransmission is scheduled after rtt + 2 times the deviation. A retransmit doubles the rtt estimate to avoid the no-update case when rtt suddenly increases. The rtt is estimated in microseconds and the granularity for retransmits is 256 microseconds. Signed-off-by: Dimitri Staessens <dimitri.staessens@ugent.be> Signed-off-by: Sander Vrijders <sander.vrijders@ugent.be>
Diffstat (limited to 'src/lib/rxmwheel.c')
-rw-r--r--src/lib/rxmwheel.c32
1 files changed, 26 insertions, 6 deletions
diff --git a/src/lib/rxmwheel.c b/src/lib/rxmwheel.c
index 395a5d8f..56ac7298 100644
--- a/src/lib/rxmwheel.c
+++ b/src/lib/rxmwheel.c
@@ -22,15 +22,16 @@
#include <ouroboros/list.h>
-#define RXMQ_S 12 /* defines #slots */
-#define RXMQ_M 15 /* defines max delay */
+#define RXMQ_S 16 /* defines #slots */
+#define RXMQ_M 24 /* defines max delay */
#define RXMQ_R (RXMQ_M - RXMQ_S) /* defines resolution */
#define RXMQ_SLOTS (1 << RXMQ_S)
#define RXMQ_MAX (1 << RXMQ_M) /* ms */
/* Small inacurracy to avoid slow division by MILLION. */
#define ts_to_ms(ts) (ts.tv_sec * 1000 + (ts.tv_nsec >> 20))
-#define ts_to_slot(ts) ((ts_to_ms(ts) >> RXMQ_R) & (RXMQ_SLOTS - 1))
+#define ts_to_us(ts) (ts.tv_sec * MILLION + (ts.tv_nsec >> 10))
+#define ts_to_slot(ts) ((ts_to_us(ts) >> RXMQ_R) & (RXMQ_SLOTS - 1))
struct rxm {
struct list_head next;
@@ -109,6 +110,21 @@ static void rxmwheel_clear(int fd)
pthread_mutex_unlock(&rw.lock);
}
+static void check_probe(struct frcti * frcti,
+ uint32_t seqno)
+{
+ /* disable rtt probe if this packet */
+
+ /* TODO: This should be locked, but lock reversal! */
+
+ if (frcti->probe && ((frcti->rttseq + 1) == seqno)) {
+ /* Backoff to avoid never updating rtt */
+ frcti->srtt_us <<= 1;
+ frcti->probe = false;
+ }
+}
+
+#define rto(frcti) (frcti->srtt_us + (frcti->mdev_us << 1))
/* Return fd on r-timer expiry. */
static int rxmwheel_move(void)
{
@@ -148,6 +164,10 @@ static int rxmwheel_move(void)
free(r);
continue;
}
+
+ /* Disable using this seqno as rto probe. */
+ check_probe(r->frcti, r->seqno);
+
/* Check for r-timer expiry. */
if (ts_to_ms(now) - r->t0 > r->frcti->r) {
int fd = r->frcti->fd;
@@ -201,7 +221,7 @@ static int rxmwheel_move(void)
r->tail = shm_du_buff_tail(sdb);
r->sdb = sdb;
- newtime = ts_to_ms(now) + (f->frcti->rto << ++r->mul);
+ newtime = ts_to_us(now) + rto(f->frcti);
rslot = (newtime >> RXMQ_R) & (RXMQ_SLOTS - 1);
list_add_tail(&r->next, &rw.wheel[rslot]);
@@ -231,7 +251,7 @@ static int rxmwheel_add(struct frcti * frcti,
pthread_mutex_lock(&rw.lock);
- r->t0 = ts_to_ms(now);
+ r->t0 = ts_to_us(now);
r->mul = 0;
r->seqno = seqno;
r->sdb = sdb;
@@ -239,7 +259,7 @@ static int rxmwheel_add(struct frcti * frcti,
r->tail = shm_du_buff_tail(sdb);
r->frcti = frcti;
- slot = ((r->t0 + frcti->rto) >> RXMQ_R) & (RXMQ_SLOTS - 1);
+ slot = ((r->t0 + rto(frcti)) >> RXMQ_R) & (RXMQ_SLOTS - 1);
list_add_tail(&r->next, &rw.wheel[slot]);