528 lines
16 KiB
C
528 lines
16 KiB
C
/*-
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* Copyright (c) 2007-2008
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* Swinburne University of Technology, Melbourne, Australia
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* Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
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* Copyright (c) 2010 The FreeBSD Foundation
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* All rights reserved.
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*
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* This software was developed at the Centre for Advanced Internet
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* Architectures, Swinburne University of Technology, by Lawrence Stewart and
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* James Healy, made possible in part by a grant from the Cisco University
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* Research Program Fund at Community Foundation Silicon Valley.
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*
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* Portions of this software were developed at the Centre for Advanced
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* Internet Architectures, Swinburne University of Technology, Melbourne,
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* Australia by David Hayes under sponsorship from the FreeBSD Foundation.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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/*
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* An implementation of the H-TCP congestion control algorithm for FreeBSD,
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* based on the Internet Draft "draft-leith-tcp-htcp-06.txt" by Leith and
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* Shorten. Originally released as part of the NewTCP research project at
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* Swinburne University of Technology's Centre for Advanced Internet
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* Architectures, Melbourne, Australia, which was made possible in part by a
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* grant from the Cisco University Research Program Fund at Community Foundation
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* Silicon Valley. More details are available at:
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* http://caia.swin.edu.au/urp/newtcp/
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include <sys/kernel.h>
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#include <sys/limits.h>
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#include <sys/malloc.h>
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#include <sys/module.h>
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#include <sys/socket.h>
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#include <sys/socketvar.h>
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#include <sys/sysctl.h>
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#include <sys/systm.h>
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#include <net/vnet.h>
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#include <netinet/tcp.h>
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#include <netinet/tcp_seq.h>
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#include <netinet/tcp_timer.h>
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#include <netinet/tcp_var.h>
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#include <netinet/cc/cc.h>
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#include <netinet/cc/cc_module.h>
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/* Fixed point math shifts. */
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#define HTCP_SHIFT 8
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#define HTCP_ALPHA_INC_SHIFT 4
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#define HTCP_INIT_ALPHA 1
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#define HTCP_DELTA_L hz /* 1 sec in ticks. */
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#define HTCP_MINBETA 128 /* 0.5 << HTCP_SHIFT. */
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#define HTCP_MAXBETA 204 /* ~0.8 << HTCP_SHIFT. */
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#define HTCP_MINROWE 26 /* ~0.1 << HTCP_SHIFT. */
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#define HTCP_MAXROWE 512 /* 2 << HTCP_SHIFT. */
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/* RTT_ref (ms) used in the calculation of alpha if RTT scaling is enabled. */
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#define HTCP_RTT_REF 100
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/* Don't trust SRTT until this many samples have been taken. */
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#define HTCP_MIN_RTT_SAMPLES 8
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/*
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* HTCP_CALC_ALPHA performs a fixed point math calculation to determine the
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* value of alpha, based on the function defined in the HTCP spec.
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*
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* i.e. 1 + 10(delta - delta_l) + ((delta - delta_l) / 2) ^ 2
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*
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* "diff" is passed in to the macro as "delta - delta_l" and is expected to be
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* in units of ticks.
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*
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* The joyousnous of fixed point maths means our function implementation looks a
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* little funky...
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*
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* In order to maintain some precision in the calculations, a fixed point shift
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* HTCP_ALPHA_INC_SHIFT is used to ensure the integer divisions don't
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* truncate the results too badly.
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*
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* The "16" value is the "1" term in the alpha function shifted up by
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* HTCP_ALPHA_INC_SHIFT
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*
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* The "160" value is the "10" multiplier in the alpha function multiplied by
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* 2^HTCP_ALPHA_INC_SHIFT
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*
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* Specifying these as constants reduces the computations required. After
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* up-shifting all the terms in the function and performing the required
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* calculations, we down-shift the final result by HTCP_ALPHA_INC_SHIFT to
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* ensure it is back in the correct range.
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*
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* The "hz" terms are required as kernels can be configured to run with
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* different tick timers, which we have to adjust for in the alpha calculation
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* (which originally was defined in terms of seconds).
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*
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* We also have to be careful to constrain the value of diff such that it won't
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* overflow whilst performing the calculation. The middle term i.e. (160 * diff)
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* / hz is the limiting factor in the calculation. We must constrain diff to be
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* less than the max size of an int divided by the constant 160 figure
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* i.e. diff < INT_MAX / 160
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*
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* NB: Changing HTCP_ALPHA_INC_SHIFT will require you to MANUALLY update the
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* constants used in this function!
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*/
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#define HTCP_CALC_ALPHA(diff) \
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((\
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(16) + \
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((160 * (diff)) / hz) + \
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(((diff) / hz) * (((diff) << HTCP_ALPHA_INC_SHIFT) / (4 * hz))) \
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) >> HTCP_ALPHA_INC_SHIFT)
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static void htcp_ack_received(struct cc_var *ccv, uint16_t type);
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static void htcp_cb_destroy(struct cc_var *ccv);
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static int htcp_cb_init(struct cc_var *ccv);
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static void htcp_cong_signal(struct cc_var *ccv, uint32_t type);
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static int htcp_mod_init(void);
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static void htcp_post_recovery(struct cc_var *ccv);
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static void htcp_recalc_alpha(struct cc_var *ccv);
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static void htcp_recalc_beta(struct cc_var *ccv);
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static void htcp_record_rtt(struct cc_var *ccv);
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static void htcp_ssthresh_update(struct cc_var *ccv);
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struct htcp {
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/* cwnd before entering cong recovery. */
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unsigned long prev_cwnd;
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/* cwnd additive increase parameter. */
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int alpha;
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/* cwnd multiplicative decrease parameter. */
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int beta;
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/* Largest rtt seen for the flow. */
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int maxrtt;
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/* Shortest rtt seen for the flow. */
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int minrtt;
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/* Time of last congestion event in ticks. */
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int t_last_cong;
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};
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static int htcp_rtt_ref;
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/*
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* The maximum number of ticks the value of diff can reach in
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* htcp_recalc_alpha() before alpha will stop increasing due to overflow.
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* See comment above HTCP_CALC_ALPHA for more info.
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*/
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static int htcp_max_diff = INT_MAX / ((1 << HTCP_ALPHA_INC_SHIFT) * 10);
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/* Per-netstack vars. */
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static VNET_DEFINE(u_int, htcp_adaptive_backoff) = 0;
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static VNET_DEFINE(u_int, htcp_rtt_scaling) = 0;
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#define V_htcp_adaptive_backoff VNET(htcp_adaptive_backoff)
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#define V_htcp_rtt_scaling VNET(htcp_rtt_scaling)
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static MALLOC_DEFINE(M_HTCP, "htcp data",
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"Per connection data required for the HTCP congestion control algorithm");
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struct cc_algo htcp_cc_algo = {
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.name = "htcp",
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.ack_received = htcp_ack_received,
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.cb_destroy = htcp_cb_destroy,
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.cb_init = htcp_cb_init,
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.cong_signal = htcp_cong_signal,
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.mod_init = htcp_mod_init,
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.post_recovery = htcp_post_recovery,
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};
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static void
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htcp_ack_received(struct cc_var *ccv, uint16_t type)
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{
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struct htcp *htcp_data;
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htcp_data = ccv->cc_data;
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htcp_record_rtt(ccv);
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/*
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* Regular ACK and we're not in cong/fast recovery and we're cwnd
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* limited and we're either not doing ABC or are slow starting or are
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* doing ABC and we've sent a cwnd's worth of bytes.
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*/
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if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) &&
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(ccv->flags & CCF_CWND_LIMITED) && (!V_tcp_do_rfc3465 ||
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CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) ||
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(V_tcp_do_rfc3465 && ccv->flags & CCF_ABC_SENTAWND))) {
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htcp_recalc_beta(ccv);
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htcp_recalc_alpha(ccv);
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/*
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* Use the logic in NewReno ack_received() for slow start and
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* for the first HTCP_DELTA_L ticks after either the flow starts
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* or a congestion event (when alpha equals 1).
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*/
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if (htcp_data->alpha == 1 ||
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CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh))
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newreno_cc_algo.ack_received(ccv, type);
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else {
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if (V_tcp_do_rfc3465) {
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/* Increment cwnd by alpha segments. */
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CCV(ccv, snd_cwnd) += htcp_data->alpha *
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CCV(ccv, t_maxseg);
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ccv->flags &= ~CCF_ABC_SENTAWND;
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} else
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/*
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* Increment cwnd by alpha/cwnd segments to
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* approximate an increase of alpha segments
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* per RTT.
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*/
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CCV(ccv, snd_cwnd) += (((htcp_data->alpha <<
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HTCP_SHIFT) / (CCV(ccv, snd_cwnd) /
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CCV(ccv, t_maxseg))) * CCV(ccv, t_maxseg))
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>> HTCP_SHIFT;
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}
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}
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}
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static void
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htcp_cb_destroy(struct cc_var *ccv)
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{
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if (ccv->cc_data != NULL)
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free(ccv->cc_data, M_HTCP);
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}
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static int
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htcp_cb_init(struct cc_var *ccv)
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{
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struct htcp *htcp_data;
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htcp_data = malloc(sizeof(struct htcp), M_HTCP, M_NOWAIT);
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if (htcp_data == NULL)
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return (ENOMEM);
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/* Init some key variables with sensible defaults. */
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htcp_data->alpha = HTCP_INIT_ALPHA;
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htcp_data->beta = HTCP_MINBETA;
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htcp_data->maxrtt = TCPTV_SRTTBASE;
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htcp_data->minrtt = TCPTV_SRTTBASE;
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htcp_data->prev_cwnd = 0;
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htcp_data->t_last_cong = ticks;
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ccv->cc_data = htcp_data;
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return (0);
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}
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/*
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* Perform any necessary tasks before we enter congestion recovery.
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*/
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static void
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htcp_cong_signal(struct cc_var *ccv, uint32_t type)
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{
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struct htcp *htcp_data;
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htcp_data = ccv->cc_data;
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switch (type) {
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case CC_NDUPACK:
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if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) {
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if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
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/*
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* Apply hysteresis to maxrtt to ensure
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* reductions in the RTT are reflected in our
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* measurements.
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*/
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htcp_data->maxrtt = (htcp_data->minrtt +
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(htcp_data->maxrtt - htcp_data->minrtt) *
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95) / 100;
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htcp_ssthresh_update(ccv);
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htcp_data->t_last_cong = ticks;
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htcp_data->prev_cwnd = CCV(ccv, snd_cwnd);
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}
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ENTER_RECOVERY(CCV(ccv, t_flags));
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}
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break;
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case CC_ECN:
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if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
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/*
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* Apply hysteresis to maxrtt to ensure reductions in
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* the RTT are reflected in our measurements.
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*/
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htcp_data->maxrtt = (htcp_data->minrtt + (htcp_data->maxrtt -
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htcp_data->minrtt) * 95) / 100;
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htcp_ssthresh_update(ccv);
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CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
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htcp_data->t_last_cong = ticks;
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htcp_data->prev_cwnd = CCV(ccv, snd_cwnd);
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ENTER_CONGRECOVERY(CCV(ccv, t_flags));
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}
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break;
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case CC_RTO:
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/*
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* Grab the current time and record it so we know when the
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* most recent congestion event was. Only record it when the
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* timeout has fired more than once, as there is a reasonable
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* chance the first one is a false alarm and may not indicate
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* congestion.
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*/
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if (CCV(ccv, t_rxtshift) >= 2)
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htcp_data->t_last_cong = ticks;
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break;
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}
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}
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static int
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htcp_mod_init(void)
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{
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htcp_cc_algo.after_idle = newreno_cc_algo.after_idle;
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/*
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* HTCP_RTT_REF is defined in ms, and t_srtt in the tcpcb is stored in
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* units of TCP_RTT_SCALE*hz. Scale HTCP_RTT_REF to be in the same units
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* as t_srtt.
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*/
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htcp_rtt_ref = (HTCP_RTT_REF * TCP_RTT_SCALE * hz) / 1000;
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return (0);
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}
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/*
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* Perform any necessary tasks before we exit congestion recovery.
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*/
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static void
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htcp_post_recovery(struct cc_var *ccv)
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{
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int pipe;
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struct htcp *htcp_data;
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pipe = 0;
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htcp_data = ccv->cc_data;
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if (IN_FASTRECOVERY(CCV(ccv, t_flags))) {
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/*
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* If inflight data is less than ssthresh, set cwnd
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* conservatively to avoid a burst of data, as suggested in the
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* NewReno RFC. Otherwise, use the HTCP method.
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*
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* XXXLAS: Find a way to do this without needing curack
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*/
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if (V_tcp_do_rfc6675_pipe)
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pipe = tcp_compute_pipe(ccv->ccvc.tcp);
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else
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pipe = CCV(ccv, snd_max) - ccv->curack;
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if (pipe < CCV(ccv, snd_ssthresh))
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CCV(ccv, snd_cwnd) = pipe + CCV(ccv, t_maxseg);
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else
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CCV(ccv, snd_cwnd) = max(1, ((htcp_data->beta *
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htcp_data->prev_cwnd / CCV(ccv, t_maxseg))
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>> HTCP_SHIFT)) * CCV(ccv, t_maxseg);
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}
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}
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static void
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htcp_recalc_alpha(struct cc_var *ccv)
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{
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struct htcp *htcp_data;
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int alpha, diff, now;
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htcp_data = ccv->cc_data;
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now = ticks;
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/*
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* If ticks has wrapped around (will happen approximately once every 49
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* days on a machine with the default kern.hz=1000) and a flow straddles
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* the wrap point, our alpha calcs will be completely wrong. We cut our
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* losses and restart alpha from scratch by setting t_last_cong = now -
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* HTCP_DELTA_L.
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*
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* This does not deflate our cwnd at all. It simply slows the rate cwnd
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* is growing by until alpha regains the value it held prior to taking
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* this drastic measure.
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*/
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if (now < htcp_data->t_last_cong)
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htcp_data->t_last_cong = now - HTCP_DELTA_L;
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diff = now - htcp_data->t_last_cong - HTCP_DELTA_L;
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/* Cap alpha if the value of diff would overflow HTCP_CALC_ALPHA(). */
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if (diff < htcp_max_diff) {
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/*
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* If it has been more than HTCP_DELTA_L ticks since congestion,
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* increase alpha according to the function defined in the spec.
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*/
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if (diff > 0) {
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alpha = HTCP_CALC_ALPHA(diff);
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/*
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* Adaptive backoff fairness adjustment:
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* 2 * (1 - beta) * alpha_raw
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*/
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if (V_htcp_adaptive_backoff)
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alpha = max(1, (2 * ((1 << HTCP_SHIFT) -
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htcp_data->beta) * alpha) >> HTCP_SHIFT);
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/*
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* RTT scaling: (RTT / RTT_ref) * alpha
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* alpha will be the raw value from HTCP_CALC_ALPHA() if
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* adaptive backoff is off, or the adjusted value if
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* adaptive backoff is on.
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*/
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if (V_htcp_rtt_scaling)
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alpha = max(1, (min(max(HTCP_MINROWE,
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(CCV(ccv, t_srtt) << HTCP_SHIFT) /
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htcp_rtt_ref), HTCP_MAXROWE) * alpha)
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>> HTCP_SHIFT);
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} else
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alpha = 1;
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htcp_data->alpha = alpha;
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}
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}
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static void
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htcp_recalc_beta(struct cc_var *ccv)
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{
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struct htcp *htcp_data;
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htcp_data = ccv->cc_data;
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/*
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* TCPTV_SRTTBASE is the initialised value of each connection's SRTT, so
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* we only calc beta if the connection's SRTT has been changed from its
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* initial value. beta is bounded to ensure it is always between
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* HTCP_MINBETA and HTCP_MAXBETA.
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*/
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if (V_htcp_adaptive_backoff && htcp_data->minrtt != TCPTV_SRTTBASE &&
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htcp_data->maxrtt != TCPTV_SRTTBASE)
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htcp_data->beta = min(max(HTCP_MINBETA,
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(htcp_data->minrtt << HTCP_SHIFT) / htcp_data->maxrtt),
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HTCP_MAXBETA);
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else
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htcp_data->beta = HTCP_MINBETA;
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}
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/*
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* Record the minimum and maximum RTT seen for the connection. These are used in
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* the calculation of beta if adaptive backoff is enabled.
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*/
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static void
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htcp_record_rtt(struct cc_var *ccv)
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{
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struct htcp *htcp_data;
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htcp_data = ccv->cc_data;
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/* XXXLAS: Should there be some hysteresis for minrtt? */
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/*
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* Record the current SRTT as our minrtt if it's the smallest we've seen
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* or minrtt is currently equal to its initialised value. Ignore SRTT
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* until a min number of samples have been taken.
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*/
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if ((CCV(ccv, t_srtt) < htcp_data->minrtt ||
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htcp_data->minrtt == TCPTV_SRTTBASE) &&
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(CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES))
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htcp_data->minrtt = CCV(ccv, t_srtt);
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/*
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* Record the current SRTT as our maxrtt if it's the largest we've
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* seen. Ignore SRTT until a min number of samples have been taken.
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*/
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if (CCV(ccv, t_srtt) > htcp_data->maxrtt
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&& CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES)
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htcp_data->maxrtt = CCV(ccv, t_srtt);
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}
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/*
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* Update the ssthresh in the event of congestion.
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*/
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static void
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htcp_ssthresh_update(struct cc_var *ccv)
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{
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struct htcp *htcp_data;
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htcp_data = ccv->cc_data;
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/*
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* On the first congestion event, set ssthresh to cwnd * 0.5, on
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* subsequent congestion events, set it to cwnd * beta.
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*/
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if (CCV(ccv, snd_ssthresh) == TCP_MAXWIN << TCP_MAX_WINSHIFT)
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CCV(ccv, snd_ssthresh) = (CCV(ccv, snd_cwnd) * HTCP_MINBETA)
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>> HTCP_SHIFT;
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else {
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htcp_recalc_beta(ccv);
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CCV(ccv, snd_ssthresh) = (CCV(ccv, snd_cwnd) * htcp_data->beta)
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>> HTCP_SHIFT;
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}
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}
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SYSCTL_DECL(_net_inet_tcp_cc_htcp);
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SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, htcp, CTLFLAG_RW,
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NULL, "H-TCP related settings");
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SYSCTL_UINT(_net_inet_tcp_cc_htcp, OID_AUTO, adaptive_backoff,
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CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(htcp_adaptive_backoff), 0,
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"enable H-TCP adaptive backoff");
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SYSCTL_UINT(_net_inet_tcp_cc_htcp, OID_AUTO, rtt_scaling,
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CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(htcp_rtt_scaling), 0,
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"enable H-TCP RTT scaling");
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DECLARE_CC_MODULE(htcp, &htcp_cc_algo);
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