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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2010-09-19 20:10:52 +0200
committerGerrit Renker <gerrit@erg.abdn.ac.uk>2010-09-21 12:14:26 +0200
commit792e6d3389061ad449429b9ba228eb758c247ea0 (patch)
tree31a238fb2fc28e465e95b7d98b5e0698461cdadf /net/dccp
parent80763dfbac4ed1e6dfe6ec08ef748e0e9aec3260 (diff)
downloadvexpress-lsk-792e6d3389061ad449429b9ba228eb758c247ea0.tar.gz
dccp tfrc/ccid-3: computing the loss rate from the Loss Event Rate
This adds a function to take care of the following, separate cases occurring in the computation of the Loss Rate p: * 1/(2^32-1) is mapped into 0% as per RFC 4342, 8.5; * 1/0 is mapped into 100%, the maximum; * to avoid that p = 1/x is rounded down to 0 when x is very large, since this means accidentally re-entering slow-start indicated by p == 0, the minimum resolution value of p is now returned instead; * a bug in ccid3_hc_rx_getsockopt is fixed: 1/0 was mapped into ~0U. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Diffstat (limited to 'net/dccp')
-rw-r--r--net/dccp/ccids/ccid3.c9
-rw-r--r--net/dccp/ccids/lib/tfrc.h1
-rw-r--r--net/dccp/ccids/lib/tfrc_equation.c14
3 files changed, 19 insertions, 5 deletions
diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index 90bc0a7da8e..9715eebf155 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -400,10 +400,10 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
/* Update loss event rate (which is scaled by 1e6) */
pinv = opt_recv->ccid3or_loss_event_rate;
- if (pinv == ~0U || pinv == 0) /* see RFC 4342, 8.5 */
+ if (pinv == 0)
hc->tx_p = 0;
- else /* can not exceed 100% */
- hc->tx_p = scaled_div(1, pinv);
+ else
+ hc->tx_p = tfrc_invert_loss_event_rate(pinv);
/*
* Update allowed sending rate X as per draft rfc3448bis-00, 4.2/3
@@ -834,8 +834,7 @@ static int ccid3_hc_rx_getsockopt(struct sock *sk, const int optname, int len,
return -EINVAL;
rx_info.tfrcrx_x_recv = hc->rx_x_recv;
rx_info.tfrcrx_rtt = hc->rx_rtt;
- rx_info.tfrcrx_p = hc->rx_pinv == 0 ? ~0U :
- scaled_div(1, hc->rx_pinv);
+ rx_info.tfrcrx_p = tfrc_invert_loss_event_rate(hc->rx_pinv);
len = sizeof(rx_info);
val = &rx_info;
break;
diff --git a/net/dccp/ccids/lib/tfrc.h b/net/dccp/ccids/lib/tfrc.h
index 01bb48e96c2..f8ee3f54977 100644
--- a/net/dccp/ccids/lib/tfrc.h
+++ b/net/dccp/ccids/lib/tfrc.h
@@ -57,6 +57,7 @@ static inline u32 tfrc_ewma(const u32 avg, const u32 newval, const u8 weight)
extern u32 tfrc_calc_x(u16 s, u32 R, u32 p);
extern u32 tfrc_calc_x_reverse_lookup(u32 fvalue);
+extern u32 tfrc_invert_loss_event_rate(u32 loss_event_rate);
extern int tfrc_tx_packet_history_init(void);
extern void tfrc_tx_packet_history_exit(void);
diff --git a/net/dccp/ccids/lib/tfrc_equation.c b/net/dccp/ccids/lib/tfrc_equation.c
index 22ca1cf0eb5..a052a4377e2 100644
--- a/net/dccp/ccids/lib/tfrc_equation.c
+++ b/net/dccp/ccids/lib/tfrc_equation.c
@@ -687,3 +687,17 @@ u32 tfrc_calc_x_reverse_lookup(u32 fvalue)
index = tfrc_binsearch(fvalue, 0);
return (index + 1) * 1000000 / TFRC_CALC_X_ARRSIZE;
}
+
+/**
+ * tfrc_invert_loss_event_rate - Compute p so that 10^6 corresponds to 100%
+ * When @loss_event_rate is large, there is a chance that p is truncated to 0.
+ * To avoid re-entering slow-start in that case, we set p = TFRC_SMALLEST_P > 0.
+ */
+u32 tfrc_invert_loss_event_rate(u32 loss_event_rate)
+{
+ if (loss_event_rate == UINT_MAX) /* see RFC 4342, 8.5 */
+ return 0;
+ if (unlikely(loss_event_rate == 0)) /* map 1/0 into 100% */
+ return 1000000;
+ return max_t(u32, scaled_div(1, loss_event_rate), TFRC_SMALLEST_P);
+}