44158306d7
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>
174 lines
6.4 KiB
C
174 lines
6.4 KiB
C
/*
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* net/dccp/ccids/ccid3.h
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*
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* Copyright (c) 2005-6 The University of Waikato, Hamilton, New Zealand.
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*
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* An implementation of the DCCP protocol
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*
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* This code has been developed by the University of Waikato WAND
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* research group. For further information please see http://www.wand.net.nz/
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* or e-mail Ian McDonald - ian.mcdonald@jandi.co.nz
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*
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* This code also uses code from Lulea University, rereleased as GPL by its
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* authors:
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* Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
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*
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* Changes to meet Linux coding standards, to make it meet latest ccid3 draft
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* and to make it work as a loadable module in the DCCP stack written by
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* Arnaldo Carvalho de Melo <acme@conectiva.com.br>.
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*
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* Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#ifndef _DCCP_CCID3_H_
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#define _DCCP_CCID3_H_
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#include <linux/list.h>
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#include <linux/time.h>
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#include <linux/types.h>
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#include <linux/tfrc.h>
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#include "../ccid.h"
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/* Two seconds as per RFC 3448 4.2 */
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#define TFRC_INITIAL_TIMEOUT (2 * USEC_PER_SEC)
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/* In usecs - half the scheduling granularity as per RFC3448 4.6 */
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#define TFRC_OPSYS_HALF_TIME_GRAN (USEC_PER_SEC / (2 * HZ))
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/* Parameter t_mbi from [RFC 3448, 4.3]: backoff interval in seconds */
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#define TFRC_T_MBI 64
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enum ccid3_options {
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TFRC_OPT_LOSS_EVENT_RATE = 192,
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TFRC_OPT_LOSS_INTERVALS = 193,
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TFRC_OPT_RECEIVE_RATE = 194,
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};
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struct ccid3_options_received {
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u64 ccid3or_seqno:48,
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ccid3or_loss_intervals_idx:16;
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u16 ccid3or_loss_intervals_len;
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u32 ccid3or_loss_event_rate;
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u32 ccid3or_receive_rate;
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};
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/* TFRC sender states */
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enum ccid3_hc_tx_states {
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TFRC_SSTATE_NO_SENT = 1,
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TFRC_SSTATE_NO_FBACK,
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TFRC_SSTATE_FBACK,
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TFRC_SSTATE_TERM,
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};
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/** struct ccid3_hc_tx_sock - CCID3 sender half-connection socket
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*
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* @ccid3hctx_x - Current sending rate
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* @ccid3hctx_x_recv - Receive rate
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* @ccid3hctx_x_calc - Calculated send rate (RFC 3448, 3.1)
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* @ccid3hctx_rtt - Estimate of current round trip time in usecs
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* @ccid3hctx_p - Current loss event rate (0-1) scaled by 1000000
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* @ccid3hctx_s - Packet size
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* @ccid3hctx_t_rto - Retransmission Timeout (RFC 3448, 3.1)
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* @ccid3hctx_t_ipi - Interpacket (send) interval (RFC 3448, 4.6)
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* @ccid3hctx_state - Sender state, one of %ccid3_hc_tx_states
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* @ccid3hctx_last_win_count - Last window counter sent
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* @ccid3hctx_t_last_win_count - Timestamp of earliest packet
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* with last_win_count value sent
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* @ccid3hctx_no_feedback_timer - Handle to no feedback timer
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* @ccid3hctx_idle - Flag indicating that sender is idling
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* @ccid3hctx_t_ld - Time last doubled during slow start
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* @ccid3hctx_t_nom - Nominal send time of next packet
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* @ccid3hctx_delta - Send timer delta
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* @ccid3hctx_hist - Packet history
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* @ccid3hctx_options_received - Parsed set of retrieved options
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*/
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struct ccid3_hc_tx_sock {
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struct tfrc_tx_info ccid3hctx_tfrc;
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#define ccid3hctx_x ccid3hctx_tfrc.tfrctx_x
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#define ccid3hctx_x_recv ccid3hctx_tfrc.tfrctx_x_recv
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#define ccid3hctx_x_calc ccid3hctx_tfrc.tfrctx_x_calc
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#define ccid3hctx_rtt ccid3hctx_tfrc.tfrctx_rtt
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#define ccid3hctx_p ccid3hctx_tfrc.tfrctx_p
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#define ccid3hctx_t_rto ccid3hctx_tfrc.tfrctx_rto
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#define ccid3hctx_t_ipi ccid3hctx_tfrc.tfrctx_ipi
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u16 ccid3hctx_s;
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enum ccid3_hc_tx_states ccid3hctx_state:8;
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u8 ccid3hctx_last_win_count;
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u8 ccid3hctx_idle;
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struct timeval ccid3hctx_t_last_win_count;
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struct timer_list ccid3hctx_no_feedback_timer;
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struct timeval ccid3hctx_t_ld;
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struct timeval ccid3hctx_t_nom;
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u32 ccid3hctx_delta;
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struct list_head ccid3hctx_hist;
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struct ccid3_options_received ccid3hctx_options_received;
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};
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/* TFRC receiver states */
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enum ccid3_hc_rx_states {
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TFRC_RSTATE_NO_DATA = 1,
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TFRC_RSTATE_DATA,
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TFRC_RSTATE_TERM = 127,
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};
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/** struct ccid3_hc_rx_sock - CCID3 receiver half-connection socket
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*
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* @ccid3hcrx_x_recv - Receiver estimate of send rate (RFC 3448 4.3)
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* @ccid3hcrx_rtt - Receiver estimate of rtt (non-standard)
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* @ccid3hcrx_p - current loss event rate (RFC 3448 5.4)
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* @ccid3hcrx_seqno_nonloss - Last received non-loss sequence number
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* @ccid3hcrx_ccval_nonloss - Last received non-loss Window CCVal
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* @ccid3hcrx_ccval_last_counter - Tracks window counter (RFC 4342, 8.1)
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* @ccid3hcrx_state - receiver state, one of %ccid3_hc_rx_states
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* @ccid3hcrx_bytes_recv - Total sum of DCCP payload bytes
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* @ccid3hcrx_tstamp_last_feedback - Time at which last feedback was sent
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* @ccid3hcrx_tstamp_last_ack - Time at which last feedback was sent
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* @ccid3hcrx_hist - Packet history
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* @ccid3hcrx_li_hist - Loss Interval History
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* @ccid3hcrx_s - Received packet size in bytes
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* @ccid3hcrx_pinv - Inverse of Loss Event Rate (RFC 4342, sec. 8.5)
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* @ccid3hcrx_elapsed_time - Time since packet reception
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*/
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struct ccid3_hc_rx_sock {
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struct tfrc_rx_info ccid3hcrx_tfrc;
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#define ccid3hcrx_x_recv ccid3hcrx_tfrc.tfrcrx_x_recv
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#define ccid3hcrx_rtt ccid3hcrx_tfrc.tfrcrx_rtt
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#define ccid3hcrx_p ccid3hcrx_tfrc.tfrcrx_p
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u64 ccid3hcrx_seqno_nonloss:48,
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ccid3hcrx_ccval_nonloss:4,
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ccid3hcrx_ccval_last_counter:4;
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enum ccid3_hc_rx_states ccid3hcrx_state:8;
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u32 ccid3hcrx_bytes_recv;
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struct timeval ccid3hcrx_tstamp_last_feedback;
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struct timeval ccid3hcrx_tstamp_last_ack;
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struct list_head ccid3hcrx_hist;
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struct list_head ccid3hcrx_li_hist;
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u16 ccid3hcrx_s;
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u32 ccid3hcrx_pinv;
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u32 ccid3hcrx_elapsed_time;
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};
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static inline struct ccid3_hc_tx_sock *ccid3_hc_tx_sk(const struct sock *sk)
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{
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return ccid_priv(dccp_sk(sk)->dccps_hc_tx_ccid);
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}
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static inline struct ccid3_hc_rx_sock *ccid3_hc_rx_sk(const struct sock *sk)
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{
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return ccid_priv(dccp_sk(sk)->dccps_hc_rx_ccid);
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}
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#endif /* _DCCP_CCID3_H_ */
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