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authorRichard Scheffenegger <rscheff@FreeBSD.org>2020-06-09 21:07:58 +0000
committerRichard Scheffenegger <rscheff@FreeBSD.org>2020-06-09 21:07:58 +0000
commit6907bbae187e11b642cf72e37e4841893f8d3126 (patch)
treefe713757ae30e8292bd87e27eef3ccf8c327cb29 /sys
parentef0b253881c9546ff88d3ed8480df7c791b3ddff (diff)
downloadsrc-6907bbae187e11b642cf72e37e4841893f8d3126.tar.gz
src-6907bbae187e11b642cf72e37e4841893f8d3126.zip
Prevent TCP Cubic to abruptly increase cwnd after slow-start
Introducing flags to track the initial Wmax dragging and exit from slow-start in TCP Cubic. This prevents sudden jumps in the caluclated cwnd by cubic, especially when the flow is application limited during slow start (cwnd can not grow as fast as expected). The downside is that cubic may remain slightly longer in the concave region before starting the convex region beyond Wmax again. Reviewed by: chengc_netapp.com, tuexen (mentor) Approved by: tuexen (mentor), rgrimes (mentor, blanket) MFC after: 3 weeks Sponsored by: NetApp, Inc. Differential Revision: https://reviews.freebsd.org/D23655
Notes
Notes: svn path=/head/; revision=361987
Diffstat (limited to 'sys')
-rw-r--r--sys/netinet/cc/cc_cubic.c28
1 files changed, 19 insertions, 9 deletions
diff --git a/sys/netinet/cc/cc_cubic.c b/sys/netinet/cc/cc_cubic.c
index 0188f2e5661d..28e3d3c51649 100644
--- a/sys/netinet/cc/cc_cubic.c
+++ b/sys/netinet/cc/cc_cubic.c
@@ -90,8 +90,10 @@ struct cubic {
unsigned long max_cwnd;
/* cwnd at the previous congestion event. */
unsigned long prev_max_cwnd;
- /* Number of congestion events. */
- uint32_t num_cong_events;
+ /* various flags */
+ uint32_t flags;
+#define CUBICFLAG_CONG_EVENT 0x00000001 /* congestion experienced */
+#define CUBICFLAG_IN_SLOWSTART 0x00000002 /* in slow start */
/* Minimum observed rtt in ticks. */
int min_rtt_ticks;
/* Mean observed rtt between congestion epochs. */
@@ -138,9 +140,10 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type)
(V_tcp_do_rfc3465 && ccv->flags & CCF_ABC_SENTAWND))) {
/* Use the logic in NewReno ack_received() for slow start. */
if (CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) ||
- cubic_data->min_rtt_ticks == TCPTV_SRTTBASE)
+ cubic_data->min_rtt_ticks == TCPTV_SRTTBASE) {
+ cubic_data->flags |= CUBICFLAG_IN_SLOWSTART;
newreno_cc_algo.ack_received(ccv, type);
- else {
+ } else {
if ((ticks_since_cong =
ticks - cubic_data->t_last_cong) < 0) {
/*
@@ -150,6 +153,11 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type)
cubic_data->t_last_cong = ticks - INT_MAX;
}
+ if (cubic_data->flags & CUBICFLAG_IN_SLOWSTART) {
+ cubic_data->flags &= ~CUBICFLAG_IN_SLOWSTART;
+ cubic_data->t_last_cong = ticks;
+ cubic_data->K = 0;
+ }
/*
* The mean RTT is used to best reflect the equations in
* the I-D. Using min_rtt in the tf_cwnd calculation
@@ -199,7 +207,7 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type)
* keep updating our current estimate of the
* max_cwnd.
*/
- if (cubic_data->num_cong_events == 0 &&
+ if (((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) &&
cubic_data->max_cwnd < CCV(ccv, snd_cwnd)) {
cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
cubic_data->K = cubic_k(cubic_data->max_cwnd /
@@ -270,9 +278,10 @@ cubic_cong_signal(struct cc_var *ccv, uint32_t type)
if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) {
if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
cubic_ssthresh_update(ccv);
- cubic_data->num_cong_events++;
+ cubic_data->flags |= CUBICFLAG_CONG_EVENT;
cubic_data->prev_max_cwnd = cubic_data->max_cwnd;
cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
+ cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg));
}
ENTER_RECOVERY(CCV(ccv, t_flags));
}
@@ -281,10 +290,11 @@ cubic_cong_signal(struct cc_var *ccv, uint32_t type)
case CC_ECN:
if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
cubic_ssthresh_update(ccv);
- cubic_data->num_cong_events++;
+ cubic_data->flags |= CUBICFLAG_CONG_EVENT;
cubic_data->prev_max_cwnd = cubic_data->max_cwnd;
cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
cubic_data->t_last_cong = ticks;
+ cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg));
CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
ENTER_CONGRECOVERY(CCV(ccv, t_flags));
}
@@ -299,7 +309,7 @@ cubic_cong_signal(struct cc_var *ccv, uint32_t type)
* congestion.
*/
if (CCV(ccv, t_rxtshift) >= 2) {
- cubic_data->num_cong_events++;
+ cubic_data->flags |= CUBICFLAG_CONG_EVENT;
cubic_data->t_last_cong = ticks;
}
break;
@@ -442,7 +452,7 @@ cubic_ssthresh_update(struct cc_var *ccv)
* On the first congestion event, set ssthresh to cwnd * 0.5, on
* subsequent congestion events, set it to cwnd * beta.
*/
- if (cubic_data->num_cong_events == 0)
+ if ((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0)
ssthresh = CCV(ccv, snd_cwnd) >> 1;
else
ssthresh = ((uint64_t)CCV(ccv, snd_cwnd) *