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-rw-r--r--net/dccp/ccids/lib/tfrc.h1
-rw-r--r--net/dccp/ccids/lib/tfrc_equation.c17
2 files changed, 16 insertions, 2 deletions
diff --git a/net/dccp/ccids/lib/tfrc.h b/net/dccp/ccids/lib/tfrc.h
index ed9857527ac..bb47146ac7d 100644
--- a/net/dccp/ccids/lib/tfrc.h
+++ b/net/dccp/ccids/lib/tfrc.h
@@ -58,6 +58,7 @@ 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 2f20a29cffe..bc3dc2b2a84 100644
--- a/net/dccp/ccids/lib/tfrc_equation.c
+++ b/net/dccp/ccids/lib/tfrc_equation.c
@@ -658,7 +658,6 @@ u32 tfrc_calc_x(u16 s, u32 R, u32 p)
result = scaled_div(s, R);
return scaled_div32(result, f);
}
-
EXPORT_SYMBOL_GPL(tfrc_calc_x);
/**
@@ -693,5 +692,19 @@ u32 tfrc_calc_x_reverse_lookup(u32 fvalue)
index = tfrc_binsearch(fvalue, 0);
return (index + 1) * 1000000 / TFRC_CALC_X_ARRSIZE;
}
-
EXPORT_SYMBOL_GPL(tfrc_calc_x_reverse_lookup);
+
+/**
+ * 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);
+}
+EXPORT_SYMBOL_GPL(tfrc_invert_loss_event_rate);