4644fda3f7
Discussed with: lstewart
473 lines
13 KiB
C
473 lines
13 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) 2014 Midori Kato <katoon@sfc.wide.ad.jp>
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* Copyright (c) 2014 The FreeBSD Foundation
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* All rights reserved.
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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 DCTCP algorithm for FreeBSD, based on
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* "Data Center TCP (DCTCP)" by M. Alizadeh, A. Greenberg, D. A. Maltz,
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* J. Padhye, P. Patel, B. Prabhakar, S. Sengupta, and M. Sridharan.,
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* in ACM Conference on SIGCOMM 2010, New York, USA,
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* Originally released as the contribution of Microsoft Research project.
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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/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_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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#define CAST_PTR_INT(X) (*((int*)(X)))
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#define MAX_ALPHA_VALUE 1024
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static VNET_DEFINE(uint32_t, dctcp_alpha) = 0;
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#define V_dctcp_alpha VNET(dctcp_alpha)
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static VNET_DEFINE(uint32_t, dctcp_shift_g) = 4;
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#define V_dctcp_shift_g VNET(dctcp_shift_g)
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static VNET_DEFINE(uint32_t, dctcp_slowstart) = 0;
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#define V_dctcp_slowstart VNET(dctcp_slowstart)
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struct dctcp {
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int bytes_ecn; /* # of marked bytes during a RTT */
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int bytes_total; /* # of acked bytes during a RTT */
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int alpha; /* the fraction of marked bytes */
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int ce_prev; /* CE state of the last segment */
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int save_sndnxt; /* end sequence number of the current window */
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int ece_curr; /* ECE flag in this segment */
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int ece_prev; /* ECE flag in the last segment */
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uint32_t num_cong_events; /* # of congestion events */
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};
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static MALLOC_DEFINE(M_dctcp, "dctcp data",
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"Per connection data required for the dctcp algorithm");
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static void dctcp_ack_received(struct cc_var *ccv, uint16_t type);
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static void dctcp_after_idle(struct cc_var *ccv);
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static void dctcp_cb_destroy(struct cc_var *ccv);
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static int dctcp_cb_init(struct cc_var *ccv);
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static void dctcp_cong_signal(struct cc_var *ccv, uint32_t type);
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static void dctcp_conn_init(struct cc_var *ccv);
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static void dctcp_post_recovery(struct cc_var *ccv);
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static void dctcp_ecnpkt_handler(struct cc_var *ccv);
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static void dctcp_update_alpha(struct cc_var *ccv);
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struct cc_algo dctcp_cc_algo = {
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.name = "dctcp",
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.ack_received = dctcp_ack_received,
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.cb_destroy = dctcp_cb_destroy,
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.cb_init = dctcp_cb_init,
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.cong_signal = dctcp_cong_signal,
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.conn_init = dctcp_conn_init,
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.post_recovery = dctcp_post_recovery,
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.ecnpkt_handler = dctcp_ecnpkt_handler,
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.after_idle = dctcp_after_idle,
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};
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static void
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dctcp_ack_received(struct cc_var *ccv, uint16_t type)
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{
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struct dctcp *dctcp_data;
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int bytes_acked = 0;
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dctcp_data = ccv->cc_data;
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if (CCV(ccv, t_flags) & TF_ECN_PERMIT) {
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/*
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* DCTCP doesn't treat receipt of ECN marked packet as a
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* congestion event. Thus, DCTCP always executes the ACK
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* processing out of congestion recovery.
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*/
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if (IN_CONGRECOVERY(CCV(ccv, t_flags))) {
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EXIT_CONGRECOVERY(CCV(ccv, t_flags));
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newreno_cc_algo.ack_received(ccv, type);
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ENTER_CONGRECOVERY(CCV(ccv, t_flags));
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} else
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newreno_cc_algo.ack_received(ccv, type);
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if (type == CC_DUPACK)
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bytes_acked = CCV(ccv, t_maxseg);
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if (type == CC_ACK)
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bytes_acked = ccv->bytes_this_ack;
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/* Update total bytes. */
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dctcp_data->bytes_total += bytes_acked;
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/* Update total marked bytes. */
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if (dctcp_data->ece_curr) {
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if (!dctcp_data->ece_prev
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&& bytes_acked > CCV(ccv, t_maxseg)) {
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dctcp_data->bytes_ecn +=
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(bytes_acked - CCV(ccv, t_maxseg));
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} else
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dctcp_data->bytes_ecn += bytes_acked;
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dctcp_data->ece_prev = 1;
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} else {
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if (dctcp_data->ece_prev
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&& bytes_acked > CCV(ccv, t_maxseg))
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dctcp_data->bytes_ecn += CCV(ccv, t_maxseg);
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dctcp_data->ece_prev = 0;
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}
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dctcp_data->ece_curr = 0;
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/*
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* Update the fraction of marked bytes at the end of
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* current window size.
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*/
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if ((IN_FASTRECOVERY(CCV(ccv, t_flags)) &&
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SEQ_GEQ(ccv->curack, CCV(ccv, snd_recover))) ||
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(!IN_FASTRECOVERY(CCV(ccv, t_flags)) &&
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SEQ_GT(ccv->curack, dctcp_data->save_sndnxt)))
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dctcp_update_alpha(ccv);
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} else
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newreno_cc_algo.ack_received(ccv, type);
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}
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static void
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dctcp_after_idle(struct cc_var *ccv)
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{
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struct dctcp *dctcp_data;
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dctcp_data = ccv->cc_data;
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/* Initialize internal parameters after idle time */
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dctcp_data->bytes_ecn = 0;
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dctcp_data->bytes_total = 0;
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dctcp_data->save_sndnxt = CCV(ccv, snd_nxt);
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dctcp_data->alpha = V_dctcp_alpha;
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dctcp_data->ece_curr = 0;
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dctcp_data->ece_prev = 0;
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dctcp_data->num_cong_events = 0;
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dctcp_cc_algo.after_idle = newreno_cc_algo.after_idle;
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}
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static void
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dctcp_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_dctcp);
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}
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static int
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dctcp_cb_init(struct cc_var *ccv)
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{
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struct dctcp *dctcp_data;
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dctcp_data = malloc(sizeof(struct dctcp), M_dctcp, M_NOWAIT|M_ZERO);
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if (dctcp_data == NULL)
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return (ENOMEM);
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/* Initialize some key variables with sensible defaults. */
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dctcp_data->bytes_ecn = 0;
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dctcp_data->bytes_total = 0;
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/*
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* When alpha is set to 0 in the beggining, DCTCP sender transfers as
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* much data as possible until the value converges which may expand the
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* queueing delay at the switch. When alpha is set to 1, queueing delay
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* is kept small.
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* Throughput-sensitive applications should have alpha = 0
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* Latency-sensitive applications should have alpha = 1
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*
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* Note: DCTCP draft suggests initial alpha to be 1 but we've decided to
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* keep it 0 as default.
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*/
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dctcp_data->alpha = V_dctcp_alpha;
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dctcp_data->save_sndnxt = 0;
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dctcp_data->ce_prev = 0;
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dctcp_data->ece_curr = 0;
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dctcp_data->ece_prev = 0;
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dctcp_data->num_cong_events = 0;
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ccv->cc_data = dctcp_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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dctcp_cong_signal(struct cc_var *ccv, uint32_t type)
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{
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struct dctcp *dctcp_data;
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u_int win, mss;
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dctcp_data = ccv->cc_data;
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win = CCV(ccv, snd_cwnd);
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mss = CCV(ccv, t_maxseg);
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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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CCV(ccv, snd_ssthresh) = mss *
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max(win / 2 / mss, 2);
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dctcp_data->num_cong_events++;
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} else {
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/* cwnd has already updated as congestion
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* recovery. Reverse cwnd value using
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* snd_cwnd_prev and recalculate snd_ssthresh
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*/
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win = CCV(ccv, snd_cwnd_prev);
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CCV(ccv, snd_ssthresh) =
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max(win / 2 / mss, 2) * mss;
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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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/*
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* Save current snd_cwnd when the host encounters both
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* congestion recovery and fast recovery.
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*/
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CCV(ccv, snd_cwnd_prev) = win;
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if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
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if (V_dctcp_slowstart &&
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dctcp_data->num_cong_events++ == 0) {
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CCV(ccv, snd_ssthresh) =
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mss * max(win / 2 / mss, 2);
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dctcp_data->alpha = MAX_ALPHA_VALUE;
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dctcp_data->bytes_ecn = 0;
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dctcp_data->bytes_total = 0;
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dctcp_data->save_sndnxt = CCV(ccv, snd_nxt);
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} else
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CCV(ccv, snd_ssthresh) = max((win - ((win *
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dctcp_data->alpha) >> 11)) / mss, 2) * mss;
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CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
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ENTER_CONGRECOVERY(CCV(ccv, t_flags));
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}
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dctcp_data->ece_curr = 1;
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break;
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case CC_RTO:
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if (CCV(ccv, t_flags) & TF_ECN_PERMIT) {
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CCV(ccv, t_flags) |= TF_ECN_SND_CWR;
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dctcp_update_alpha(ccv);
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dctcp_data->save_sndnxt += CCV(ccv, t_maxseg);
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dctcp_data->num_cong_events++;
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}
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break;
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}
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}
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static void
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dctcp_conn_init(struct cc_var *ccv)
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{
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struct dctcp *dctcp_data;
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dctcp_data = ccv->cc_data;
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if (CCV(ccv, t_flags) & TF_ECN_PERMIT)
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dctcp_data->save_sndnxt = CCV(ccv, snd_nxt);
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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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dctcp_post_recovery(struct cc_var *ccv)
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{
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dctcp_cc_algo.post_recovery = newreno_cc_algo.post_recovery;
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if (CCV(ccv, t_flags) & TF_ECN_PERMIT)
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dctcp_update_alpha(ccv);
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}
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/*
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* Execute an additional ECN processing using ECN field in IP header and the CWR
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* bit in TCP header.
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*
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* delay_ack == 0 - Delayed ACK disabled
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* delay_ack == 1 - Delayed ACK enabled
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*/
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static void
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dctcp_ecnpkt_handler(struct cc_var *ccv)
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{
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struct dctcp *dctcp_data;
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uint32_t ccflag;
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int delay_ack;
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dctcp_data = ccv->cc_data;
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ccflag = ccv->flags;
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delay_ack = 1;
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/*
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* DCTCP responses an ACK immediately when the CE state
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* in between this segment and the last segment is not same.
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*/
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if (ccflag & CCF_IPHDR_CE) {
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if (!dctcp_data->ce_prev && (ccflag & CCF_DELACK))
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delay_ack = 0;
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dctcp_data->ce_prev = 1;
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CCV(ccv, t_flags) |= TF_ECN_SND_ECE;
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} else {
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if (dctcp_data->ce_prev && (ccflag & CCF_DELACK))
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delay_ack = 0;
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dctcp_data->ce_prev = 0;
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CCV(ccv, t_flags) &= ~TF_ECN_SND_ECE;
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}
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/* DCTCP sets delayed ack when this segment sets the CWR flag. */
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if ((ccflag & CCF_DELACK) && (ccflag & CCF_TCPHDR_CWR))
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delay_ack = 1;
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if (delay_ack == 0)
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ccv->flags |= CCF_ACKNOW;
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else
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ccv->flags &= ~CCF_ACKNOW;
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}
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/*
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* Update the fraction of marked bytes represented as 'alpha'.
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* Also initialize several internal parameters at the end of this function.
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*/
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static void
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dctcp_update_alpha(struct cc_var *ccv)
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{
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struct dctcp *dctcp_data;
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int alpha_prev;
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dctcp_data = ccv->cc_data;
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alpha_prev = dctcp_data->alpha;
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dctcp_data->bytes_total = max(dctcp_data->bytes_total, 1);
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/*
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* Update alpha: alpha = (1 - g) * alpha + g * F.
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* Here:
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* g is weight factor
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* recommaded to be set to 1/16
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* small g = slow convergence between competitive DCTCP flows
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* large g = impacts low utilization of bandwidth at switches
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* F is fraction of marked segments in last RTT
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* updated every RTT
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* Alpha must be round to 0 - MAX_ALPHA_VALUE.
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*/
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dctcp_data->alpha = min(alpha_prev - (alpha_prev >> V_dctcp_shift_g) +
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(dctcp_data->bytes_ecn << (10 - V_dctcp_shift_g)) /
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dctcp_data->bytes_total, MAX_ALPHA_VALUE);
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/* Initialize internal parameters for next alpha calculation */
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dctcp_data->bytes_ecn = 0;
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dctcp_data->bytes_total = 0;
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dctcp_data->save_sndnxt = CCV(ccv, snd_nxt);
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}
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static int
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dctcp_alpha_handler(SYSCTL_HANDLER_ARGS)
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{
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uint32_t new;
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int error;
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new = V_dctcp_alpha;
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error = sysctl_handle_int(oidp, &new, 0, req);
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if (error == 0 && req->newptr != NULL) {
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if (CAST_PTR_INT(req->newptr) > 1)
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error = EINVAL;
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else {
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if (new > MAX_ALPHA_VALUE)
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V_dctcp_alpha = MAX_ALPHA_VALUE;
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else
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V_dctcp_alpha = new;
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}
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}
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return (error);
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}
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static int
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dctcp_shift_g_handler(SYSCTL_HANDLER_ARGS)
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{
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uint32_t new;
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int error;
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new = V_dctcp_shift_g;
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error = sysctl_handle_int(oidp, &new, 0, req);
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if (error == 0 && req->newptr != NULL) {
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if (CAST_PTR_INT(req->newptr) > 1)
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error = EINVAL;
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else
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V_dctcp_shift_g = new;
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}
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return (error);
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}
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static int
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dctcp_slowstart_handler(SYSCTL_HANDLER_ARGS)
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{
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uint32_t new;
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int error;
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new = V_dctcp_slowstart;
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error = sysctl_handle_int(oidp, &new, 0, req);
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if (error == 0 && req->newptr != NULL) {
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if (CAST_PTR_INT(req->newptr) > 1)
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error = EINVAL;
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else
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V_dctcp_slowstart = new;
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}
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return (error);
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}
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SYSCTL_DECL(_net_inet_tcp_cc_dctcp);
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SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, dctcp, CTLFLAG_RW, NULL,
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"dctcp congestion control related settings");
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SYSCTL_PROC(_net_inet_tcp_cc_dctcp, OID_AUTO, alpha,
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CTLFLAG_VNET|CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(dctcp_alpha), 0,
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&dctcp_alpha_handler,
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"IU", "dctcp alpha parameter");
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SYSCTL_PROC(_net_inet_tcp_cc_dctcp, OID_AUTO, shift_g,
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CTLFLAG_VNET|CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(dctcp_shift_g), 4,
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&dctcp_shift_g_handler,
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"IU", "dctcp shift parameter");
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SYSCTL_PROC(_net_inet_tcp_cc_dctcp, OID_AUTO, slowstart,
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CTLFLAG_VNET|CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(dctcp_slowstart), 0,
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&dctcp_slowstart_handler,
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"IU", "half CWND reduction after the first slow start");
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DECLARE_CC_MODULE(dctcp, &dctcp_cc_algo);
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