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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2006-12-03 14:53:07 -0200
committerArnaldo Carvalho de Melo <acme@mandriva.com>2006-12-03 14:53:07 -0200
commit44158306d756c88272c8faf243ca68897498e219 (patch)
treeb5406da158950a099336a67c507a0dd55c04fa25 /net/dccp/ccids/ccid3.h
parent006042d7e1a0aae35c9dd9eb8ec71fa379679adb (diff)
[DCCP] ccid3: Deprecate TFRC_SMALLEST_P
This patch deprecates the existing use of an arbitrary value TFRC_SMALLEST_P for low-threshold values of p. This avoids masking low-resolution errors. Instead, the code now checks against real boundaries (implemented by preceding patch) and provides warnings whenever a real value falls below the threshold. If such messages are observed, it is a better solution to take this as an indication that the lookup table needs to be re-engineered. Changelog: ---------- This patch * makes handling all TFRC resolution errors local to the TFRC library * removes unnecessary test whether X_calc is 'infinity' due to p==0 -- this condition is already caught by tfrc_calc_x() * removes setting ccid3hctx_p = TFRC_SMALLEST_P in ccid3_hc_tx_packet_recv since this is now done by the TFRC library * updates BUG_ON test in ccid3_hc_tx_no_feedback_timer to take into account that p now is either 0 (and then X_calc is irrelevant), or it is > 0; since the handling of TFRC_SMALLEST_P is now taken care of in the tfrc library Justification: -------------- The TFRC code uses a lookup table which has a bounded resolution. The lowest possible value of the loss event rate `p' which can be resolved is currently 0.0001. Substituting this lower threshold for p when p is less than 0.0001 results in a huge, exponentially-growing error. The error can be computed by the following formula: (f(0.0001) - f(p))/f(p) * 100 for p < 0.0001 Currently the solution is to use an (arbitrary) value TFRC_SMALLEST_P = 40 * 1E-6 = 0.00004 and to consider all values below this value as `virtually zero'. Due to the exponentially growing resolution error, this is not a good idea, since it hides the fact that the table can not resolve practically occurring cases. Already at p == TFRC_SMALLEST_P, the error is as high as 58.19%! Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz> Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Diffstat (limited to 'net/dccp/ccids/ccid3.h')
-rw-r--r--net/dccp/ccids/ccid3.h2
1 files changed, 0 insertions, 2 deletions
diff --git a/net/dccp/ccids/ccid3.h b/net/dccp/ccids/ccid3.h
index 27cb20ae1da..07596d704ef 100644
--- a/net/dccp/ccids/ccid3.h
+++ b/net/dccp/ccids/ccid3.h
@@ -51,8 +51,6 @@
/* Parameter t_mbi from [RFC 3448, 4.3]: backoff interval in seconds */
#define TFRC_T_MBI 64
-#define TFRC_SMALLEST_P 40
-
enum ccid3_options {
TFRC_OPT_LOSS_EVENT_RATE = 192,
TFRC_OPT_LOSS_INTERVALS = 193,