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| author | glebius <glebius@FreeBSD.org> | 2007-02-02 09:45:23 +0000 |
|---|---|---|
| committer | glebius <glebius@FreeBSD.org> | 2007-02-02 09:45:23 +0000 |
| commit | fd07387e0439f7340a0f3b8d0e5b3733b6ef827b (patch) | |
| tree | 3299cfc5f0bbf16fc0d8dca3b98a8105287d3d6e /sys/netgraph | |
| parent | 325d4d7fdaa90f6cd1f3135dea61dec9ece00f8f (diff) | |
| download | FreeBSD-src-fd07387e0439f7340a0f3b8d0e5b3733b6ef827b.zip FreeBSD-src-fd07387e0439f7340a0f3b8d0e5b3733b6ef827b.tar.gz | |
Quoting Alexander:
Formulas described in RFC require high precision of floating point.
Formulas of integer math implemented in ng_pptpgre give mistake in range
of +0-7ms on RTT and +0-3ms on deviation. This leads to significant
underestimation of real packet RTT.
I have made a very simple patch to reduce mistake to +4-3ms on RTT and
+2-1ms on deviation. Mistake in RTT is not good, but gets covered by
deviation. To cover worst possible negative mistake in deviation I have
added 2ms to it. Also this 2 ms cover the case when measured deviation
is so small (about zero) that it can interfere with process scheduling
delays or weather on Mars.
My tests show decreasing of packet losses on 20ms RTT link from 2.5% to
0.3% while speed increased un 1/3.
Reviewed by: archie
Diffstat (limited to 'sys/netgraph')
| -rw-r--r-- | sys/netgraph/ng_pptpgre.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/sys/netgraph/ng_pptpgre.c b/sys/netgraph/ng_pptpgre.c index 4c39256..5a6bf8b 100644 --- a/sys/netgraph/ng_pptpgre.c +++ b/sys/netgraph/ng_pptpgre.c @@ -132,8 +132,8 @@ typedef u_int64_t pptptime_t; #define PPTP_MAX_ACK_DELAY (PPTP_TIME_SCALE / 2) /* 500 milliseconds */ /* See RFC 2637 section 4.4 */ -#define PPTP_ACK_ALPHA(x) ((x) >> 3) /* alpha = 0.125 */ -#define PPTP_ACK_BETA(x) ((x) >> 2) /* beta = 0.25 */ +#define PPTP_ACK_ALPHA(x) (((x) + 4) >> 3) /* alpha = 0.125 */ +#define PPTP_ACK_BETA(x) (((x) + 2) >> 2) /* beta = 0.25 */ #define PPTP_ACK_CHI(x) ((x) << 2) /* chi = 4 */ #define PPTP_ACK_DELTA(x) ((x) << 1) /* delta = 2 */ @@ -676,7 +676,8 @@ ng_pptpgre_recv(node_p node, item_p item) if (diff < 0) diff = -diff; a->dev += PPTP_ACK_BETA(diff - a->dev); - a->ato = a->rtt + PPTP_ACK_CHI(a->dev); + /* +2 to compensate low precision of int math */ + a->ato = a->rtt + PPTP_ACK_CHI(a->dev + 2); if (a->ato > PPTP_MAX_TIMEOUT) a->ato = PPTP_MAX_TIMEOUT; if (a->ato < PPTP_MIN_TIMEOUT) @@ -827,7 +828,7 @@ ng_pptpgre_recv_ack_timeout(node_p node, hook_p hook, void *arg1, int arg2) /* Update adaptive timeout stuff */ priv->stats.recvAckTimeouts++; - a->rtt = PPTP_ACK_DELTA(a->rtt); + a->rtt = PPTP_ACK_DELTA(a->rtt) + 1; /* +1 to avoid delta*0 case */ a->ato = a->rtt + PPTP_ACK_CHI(a->dev); if (a->ato > PPTP_MAX_TIMEOUT) a->ato = PPTP_MAX_TIMEOUT; |
