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author | Gerrit Renker <gerrit@erg.abdn.ac.uk> | 2010-09-19 18:10:52 (GMT) |
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committer | Gerrit Renker <gerrit@erg.abdn.ac.uk> | 2010-09-21 10:14:26 (GMT) |
commit | 792e6d3389061ad449429b9ba228eb758c247ea0 (patch) | |
tree | 31a238fb2fc28e465e95b7d98b5e0698461cdadf /net/dccp/ccids/lib | |
parent | 80763dfbac4ed1e6dfe6ec08ef748e0e9aec3260 (diff) | |
download | linux-fsl-qoriq-792e6d3389061ad449429b9ba228eb758c247ea0.tar.xz |
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/ccids/lib')
-rw-r--r-- | net/dccp/ccids/lib/tfrc.h | 1 | ||||
-rw-r--r-- | net/dccp/ccids/lib/tfrc_equation.c | 14 |
2 files changed, 15 insertions, 0 deletions
diff --git a/net/dccp/ccids/lib/tfrc.h b/net/dccp/ccids/lib/tfrc.h index 01bb48e..f8ee3f5 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 22ca1cf..a052a43 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); +} |