2 * Copyright (c) 2007-2008
3 * Swinburne University of Technology, Melbourne, Australia
4 * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
5 * Copyright (c) 2014 Midori Kato <katoon@sfc.wide.ad.jp>
6 * Copyright (c) 2014 The FreeBSD Foundation
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * An implementation of the DCTCP algorithm for FreeBSD, based on
33 * "Data Center TCP (DCTCP)" by M. Alizadeh, A. Greenberg, D. A. Maltz,
34 * J. Padhye, P. Patel, B. Prabhakar, S. Sengupta, and M. Sridharan.,
35 * in ACM Conference on SIGCOMM 2010, New York, USA,
36 * Originally released as the contribution of Microsoft Research project.
39 #include <sys/cdefs.h>
40 __FBSDID("$FreeBSD$");
42 #include <sys/param.h>
43 #include <sys/kernel.h>
44 #include <sys/malloc.h>
45 #include <sys/module.h>
46 #include <sys/socket.h>
47 #include <sys/socketvar.h>
48 #include <sys/sysctl.h>
49 #include <sys/systm.h>
53 #include <netinet/tcp.h>
54 #include <netinet/tcp_seq.h>
55 #include <netinet/tcp_var.h>
56 #include <netinet/cc/cc.h>
57 #include <netinet/cc/cc_module.h>
59 #define CAST_PTR_INT(X) (*((int*)(X)))
61 #define MAX_ALPHA_VALUE 1024
62 static VNET_DEFINE(uint32_t, dctcp_alpha) = 0;
63 #define V_dctcp_alpha VNET(dctcp_alpha)
64 static VNET_DEFINE(uint32_t, dctcp_shift_g) = 4;
65 #define V_dctcp_shift_g VNET(dctcp_shift_g)
66 static VNET_DEFINE(uint32_t, dctcp_slowstart) = 0;
67 #define V_dctcp_slowstart VNET(dctcp_slowstart)
70 int bytes_ecn; /* # of marked bytes during a RTT */
71 int bytes_total; /* # of acked bytes during a RTT */
72 int alpha; /* the fraction of marked bytes */
73 int ce_prev; /* CE state of the last segment */
74 int save_sndnxt; /* end sequence number of the current window */
75 int ece_curr; /* ECE flag in this segment */
76 int ece_prev; /* ECE flag in the last segment */
77 uint32_t num_cong_events; /* # of congestion events */
80 static MALLOC_DEFINE(M_dctcp, "dctcp data",
81 "Per connection data required for the dctcp algorithm");
83 static void dctcp_ack_received(struct cc_var *ccv, uint16_t type);
84 static void dctcp_after_idle(struct cc_var *ccv);
85 static void dctcp_cb_destroy(struct cc_var *ccv);
86 static int dctcp_cb_init(struct cc_var *ccv);
87 static void dctcp_cong_signal(struct cc_var *ccv, uint32_t type);
88 static void dctcp_conn_init(struct cc_var *ccv);
89 static void dctcp_post_recovery(struct cc_var *ccv);
90 static void dctcp_ecnpkt_handler(struct cc_var *ccv);
91 static void dctcp_update_alpha(struct cc_var *ccv);
93 struct cc_algo dctcp_cc_algo = {
95 .ack_received = dctcp_ack_received,
96 .cb_destroy = dctcp_cb_destroy,
97 .cb_init = dctcp_cb_init,
98 .cong_signal = dctcp_cong_signal,
99 .conn_init = dctcp_conn_init,
100 .post_recovery = dctcp_post_recovery,
101 .ecnpkt_handler = dctcp_ecnpkt_handler,
102 .after_idle = dctcp_after_idle,
106 dctcp_ack_received(struct cc_var *ccv, uint16_t type)
108 struct dctcp *dctcp_data;
111 dctcp_data = ccv->cc_data;
113 if (CCV(ccv, t_flags) & TF_ECN_PERMIT) {
115 * DCTCP doesn't treat receipt of ECN marked packet as a
116 * congestion event. Thus, DCTCP always executes the ACK
117 * processing out of congestion recovery.
119 if (IN_CONGRECOVERY(CCV(ccv, t_flags))) {
120 EXIT_CONGRECOVERY(CCV(ccv, t_flags));
121 newreno_cc_algo.ack_received(ccv, type);
122 ENTER_CONGRECOVERY(CCV(ccv, t_flags));
124 newreno_cc_algo.ack_received(ccv, type);
126 if (type == CC_DUPACK)
127 bytes_acked = CCV(ccv, t_maxseg);
130 bytes_acked = ccv->bytes_this_ack;
132 /* Update total bytes. */
133 dctcp_data->bytes_total += bytes_acked;
135 /* Update total marked bytes. */
136 if (dctcp_data->ece_curr) {
137 if (!dctcp_data->ece_prev
138 && bytes_acked > CCV(ccv, t_maxseg)) {
139 dctcp_data->bytes_ecn +=
140 (bytes_acked - CCV(ccv, t_maxseg));
142 dctcp_data->bytes_ecn += bytes_acked;
143 dctcp_data->ece_prev = 1;
145 if (dctcp_data->ece_prev
146 && bytes_acked > CCV(ccv, t_maxseg))
147 dctcp_data->bytes_ecn += CCV(ccv, t_maxseg);
148 dctcp_data->ece_prev = 0;
150 dctcp_data->ece_curr = 0;
153 * Update the fraction of marked bytes at the end of
154 * current window size.
156 if ((IN_FASTRECOVERY(CCV(ccv, t_flags)) &&
157 SEQ_GEQ(ccv->curack, CCV(ccv, snd_recover))) ||
158 (!IN_FASTRECOVERY(CCV(ccv, t_flags)) &&
159 SEQ_GT(ccv->curack, dctcp_data->save_sndnxt)))
160 dctcp_update_alpha(ccv);
162 newreno_cc_algo.ack_received(ccv, type);
166 dctcp_after_idle(struct cc_var *ccv)
168 struct dctcp *dctcp_data;
170 dctcp_data = ccv->cc_data;
172 /* Initialize internal parameters after idle time */
173 dctcp_data->bytes_ecn = 0;
174 dctcp_data->bytes_total = 0;
175 dctcp_data->save_sndnxt = CCV(ccv, snd_nxt);
176 dctcp_data->alpha = V_dctcp_alpha;
177 dctcp_data->ece_curr = 0;
178 dctcp_data->ece_prev = 0;
179 dctcp_data->num_cong_events = 0;
181 dctcp_cc_algo.after_idle = newreno_cc_algo.after_idle;
185 dctcp_cb_destroy(struct cc_var *ccv)
187 if (ccv->cc_data != NULL)
188 free(ccv->cc_data, M_dctcp);
192 dctcp_cb_init(struct cc_var *ccv)
194 struct dctcp *dctcp_data;
196 dctcp_data = malloc(sizeof(struct dctcp), M_dctcp, M_NOWAIT|M_ZERO);
198 if (dctcp_data == NULL)
201 /* Initialize some key variables with sensible defaults. */
202 dctcp_data->bytes_ecn = 0;
203 dctcp_data->bytes_total = 0;
205 * When alpha is set to 0 in the beginning, DCTCP sender transfers as
206 * much data as possible until the value converges which may expand the
207 * queueing delay at the switch. When alpha is set to 1, queueing delay
209 * Throughput-sensitive applications should have alpha = 0
210 * Latency-sensitive applications should have alpha = 1
212 * Note: DCTCP draft suggests initial alpha to be 1 but we've decided to
213 * keep it 0 as default.
215 dctcp_data->alpha = V_dctcp_alpha;
216 dctcp_data->save_sndnxt = 0;
217 dctcp_data->ce_prev = 0;
218 dctcp_data->ece_curr = 0;
219 dctcp_data->ece_prev = 0;
220 dctcp_data->num_cong_events = 0;
222 ccv->cc_data = dctcp_data;
227 * Perform any necessary tasks before we enter congestion recovery.
230 dctcp_cong_signal(struct cc_var *ccv, uint32_t type)
232 struct dctcp *dctcp_data;
233 uint32_t cwin, ssthresh_on_loss;
236 dctcp_data = ccv->cc_data;
237 cwin = CCV(ccv, snd_cwnd);
238 mss = CCV(ccv, t_maxseg);
240 max((CCV(ccv, snd_max) - CCV(ccv, snd_una)) / 2 / mss, 2)
245 if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) {
246 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
247 CCV(ccv, snd_ssthresh) = ssthresh_on_loss;
248 dctcp_data->num_cong_events++;
250 /* cwnd has already updated as congestion
251 * recovery. Reverse cwnd value using
252 * snd_cwnd_prev and recalculate snd_ssthresh
254 cwin = CCV(ccv, snd_cwnd_prev);
255 CCV(ccv, snd_ssthresh) = ssthresh_on_loss;
257 ENTER_RECOVERY(CCV(ccv, t_flags));
262 * Save current snd_cwnd when the host encounters both
263 * congestion recovery and fast recovery.
265 CCV(ccv, snd_cwnd_prev) = cwin;
266 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
267 if (V_dctcp_slowstart &&
268 dctcp_data->num_cong_events++ == 0) {
269 CCV(ccv, snd_ssthresh) = ssthresh_on_loss;
270 dctcp_data->alpha = MAX_ALPHA_VALUE;
271 dctcp_data->bytes_ecn = 0;
272 dctcp_data->bytes_total = 0;
273 dctcp_data->save_sndnxt = CCV(ccv, snd_nxt);
275 CCV(ccv, snd_ssthresh) = max((cwin - ((cwin *
276 dctcp_data->alpha) >> 11)) / mss, 2) * mss;
277 CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
278 ENTER_CONGRECOVERY(CCV(ccv, t_flags));
280 dctcp_data->ece_curr = 1;
283 if (CCV(ccv, t_flags) & TF_ECN_PERMIT) {
284 CCV(ccv, t_flags) |= TF_ECN_SND_CWR;
285 dctcp_update_alpha(ccv);
286 dctcp_data->save_sndnxt += CCV(ccv, t_maxseg);
287 dctcp_data->num_cong_events++;
288 CCV(ccv, snd_ssthresh) = ssthresh_on_loss;
289 CCV(ccv, snd_cwnd) = mss;
296 dctcp_conn_init(struct cc_var *ccv)
298 struct dctcp *dctcp_data;
300 dctcp_data = ccv->cc_data;
302 if (CCV(ccv, t_flags) & TF_ECN_PERMIT)
303 dctcp_data->save_sndnxt = CCV(ccv, snd_nxt);
307 * Perform any necessary tasks before we exit congestion recovery.
310 dctcp_post_recovery(struct cc_var *ccv)
312 dctcp_cc_algo.post_recovery = newreno_cc_algo.post_recovery;
314 if (CCV(ccv, t_flags) & TF_ECN_PERMIT)
315 dctcp_update_alpha(ccv);
319 * Execute an additional ECN processing using ECN field in IP header and the CWR
322 * delay_ack == 0 - Delayed ACK disabled
323 * delay_ack == 1 - Delayed ACK enabled
327 dctcp_ecnpkt_handler(struct cc_var *ccv)
329 struct dctcp *dctcp_data;
333 dctcp_data = ccv->cc_data;
338 * DCTCP responses an ACK immediately when the CE state
339 * in between this segment and the last segment is not same.
341 if (ccflag & CCF_IPHDR_CE) {
342 if (!dctcp_data->ce_prev && (ccflag & CCF_DELACK))
344 dctcp_data->ce_prev = 1;
345 CCV(ccv, t_flags) |= TF_ECN_SND_ECE;
347 if (dctcp_data->ce_prev && (ccflag & CCF_DELACK))
349 dctcp_data->ce_prev = 0;
350 CCV(ccv, t_flags) &= ~TF_ECN_SND_ECE;
353 /* DCTCP sets delayed ack when this segment sets the CWR flag. */
354 if ((ccflag & CCF_DELACK) && (ccflag & CCF_TCPHDR_CWR))
358 ccv->flags |= CCF_ACKNOW;
360 ccv->flags &= ~CCF_ACKNOW;
364 * Update the fraction of marked bytes represented as 'alpha'.
365 * Also initialize several internal parameters at the end of this function.
368 dctcp_update_alpha(struct cc_var *ccv)
370 struct dctcp *dctcp_data;
373 dctcp_data = ccv->cc_data;
374 alpha_prev = dctcp_data->alpha;
375 dctcp_data->bytes_total = max(dctcp_data->bytes_total, 1);
378 * Update alpha: alpha = (1 - g) * alpha + g * F.
381 * recommaded to be set to 1/16
382 * small g = slow convergence between competitive DCTCP flows
383 * large g = impacts low utilization of bandwidth at switches
384 * F is fraction of marked segments in last RTT
386 * Alpha must be round to 0 - MAX_ALPHA_VALUE.
388 dctcp_data->alpha = min(alpha_prev - (alpha_prev >> V_dctcp_shift_g) +
389 (dctcp_data->bytes_ecn << (10 - V_dctcp_shift_g)) /
390 dctcp_data->bytes_total, MAX_ALPHA_VALUE);
392 /* Initialize internal parameters for next alpha calculation */
393 dctcp_data->bytes_ecn = 0;
394 dctcp_data->bytes_total = 0;
395 dctcp_data->save_sndnxt = CCV(ccv, snd_nxt);
399 dctcp_alpha_handler(SYSCTL_HANDLER_ARGS)
405 error = sysctl_handle_int(oidp, &new, 0, req);
406 if (error == 0 && req->newptr != NULL) {
407 if (CAST_PTR_INT(req->newptr) > 1)
410 if (new > MAX_ALPHA_VALUE)
411 V_dctcp_alpha = MAX_ALPHA_VALUE;
421 dctcp_shift_g_handler(SYSCTL_HANDLER_ARGS)
426 new = V_dctcp_shift_g;
427 error = sysctl_handle_int(oidp, &new, 0, req);
428 if (error == 0 && req->newptr != NULL) {
429 if (CAST_PTR_INT(req->newptr) > 1)
432 V_dctcp_shift_g = new;
439 dctcp_slowstart_handler(SYSCTL_HANDLER_ARGS)
444 new = V_dctcp_slowstart;
445 error = sysctl_handle_int(oidp, &new, 0, req);
446 if (error == 0 && req->newptr != NULL) {
447 if (CAST_PTR_INT(req->newptr) > 1)
450 V_dctcp_slowstart = new;
456 SYSCTL_DECL(_net_inet_tcp_cc_dctcp);
457 SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, dctcp, CTLFLAG_RW, NULL,
458 "dctcp congestion control related settings");
460 SYSCTL_PROC(_net_inet_tcp_cc_dctcp, OID_AUTO, alpha,
461 CTLFLAG_VNET|CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(dctcp_alpha), 0,
462 &dctcp_alpha_handler,
463 "IU", "dctcp alpha parameter");
465 SYSCTL_PROC(_net_inet_tcp_cc_dctcp, OID_AUTO, shift_g,
466 CTLFLAG_VNET|CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(dctcp_shift_g), 4,
467 &dctcp_shift_g_handler,
468 "IU", "dctcp shift parameter");
470 SYSCTL_PROC(_net_inet_tcp_cc_dctcp, OID_AUTO, slowstart,
471 CTLFLAG_VNET|CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(dctcp_slowstart), 0,
472 &dctcp_slowstart_handler,
473 "IU", "half CWND reduction after the first slow start");
475 DECLARE_CC_MODULE(dctcp, &dctcp_cc_algo);