1 | #ifndef __NET_SCHED_CODEL_IMPL_H |
---|---|

2 | #define __NET_SCHED_CODEL_IMPL_H |

3 | |

4 | /* |

5 | * Codel - The Controlled-Delay Active Queue Management algorithm |

6 | * |

7 | * Copyright (C) 2011-2012 Kathleen Nichols <nichols@pollere.com> |

8 | * Copyright (C) 2011-2012 Van Jacobson <van@pollere.net> |

9 | * Copyright (C) 2012 Michael D. Taht <dave.taht@bufferbloat.net> |

10 | * Copyright (C) 2012,2015 Eric Dumazet <edumazet@google.com> |

11 | * |

12 | * Redistribution and use in source and binary forms, with or without |

13 | * modification, are permitted provided that the following conditions |

14 | * are met: |

15 | * 1. Redistributions of source code must retain the above copyright |

16 | * notice, this list of conditions, and the following disclaimer, |

17 | * without modification. |

18 | * 2. Redistributions in binary form must reproduce the above copyright |

19 | * notice, this list of conditions and the following disclaimer in the |

20 | * documentation and/or other materials provided with the distribution. |

21 | * 3. The names of the authors may not be used to endorse or promote products |

22 | * derived from this software without specific prior written permission. |

23 | * |

24 | * Alternatively, provided that this notice is retained in full, this |

25 | * software may be distributed under the terms of the GNU General |

26 | * Public License ("GPL") version 2, in which case the provisions of the |

27 | * GPL apply INSTEAD OF those given above. |

28 | * |

29 | * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |

30 | * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |

31 | * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |

32 | * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |

33 | * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |

34 | * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |

35 | * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |

36 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |

37 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |

38 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |

39 | * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH |

40 | * DAMAGE. |

41 | * |

42 | */ |

43 | |

44 | /* Controlling Queue Delay (CoDel) algorithm |

45 | * ========================================= |

46 | * Source : Kathleen Nichols and Van Jacobson |

47 | * http://queue.acm.org/detail.cfm?id=2209336 |

48 | * |

49 | * Implemented on linux by Dave Taht and Eric Dumazet |

50 | */ |

51 | |

52 | static void codel_params_init(struct codel_params *params) |

53 | { |

54 | params->interval = MS2TIME(100); |

55 | params->target = MS2TIME(5); |

56 | params->ce_threshold = CODEL_DISABLED_THRESHOLD; |

57 | params->ecn = false; |

58 | } |

59 | |

60 | static void codel_vars_init(struct codel_vars *vars) |

61 | { |

62 | memset(vars, 0, sizeof(*vars)); |

63 | } |

64 | |

65 | static void codel_stats_init(struct codel_stats *stats) |

66 | { |

67 | stats->maxpacket = 0; |

68 | } |

69 | |

70 | /* |

71 | * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots |

72 | * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2) |

73 | * |

74 | * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32 |

75 | */ |

76 | static void codel_Newton_step(struct codel_vars *vars) |

77 | { |

78 | u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT; |

79 | u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32; |

80 | u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2); |

81 | |

82 | val >>= 2; /* avoid overflow in following multiply */ |

83 | val = (val * invsqrt) >> (32 - 2 + 1); |

84 | |

85 | vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT; |

86 | } |

87 | |

88 | /* |

89 | * CoDel control_law is t + interval/sqrt(count) |

90 | * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid |

91 | * both sqrt() and divide operation. |

92 | */ |

93 | static codel_time_t codel_control_law(codel_time_t t, |

94 | codel_time_t interval, |

95 | u32 rec_inv_sqrt) |

96 | { |

97 | return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT); |

98 | } |

99 | |

100 | static bool codel_should_drop(const struct sk_buff *skb, |

101 | void *ctx, |

102 | struct codel_vars *vars, |

103 | struct codel_params *params, |

104 | struct codel_stats *stats, |

105 | codel_skb_len_t skb_len_func, |

106 | codel_skb_time_t skb_time_func, |

107 | u32 *backlog, |

108 | codel_time_t now) |

109 | { |

110 | bool ok_to_drop; |

111 | u32 skb_len; |

112 | |

113 | if (!skb) { |

114 | vars->first_above_time = 0; |

115 | return false; |

116 | } |

117 | |

118 | skb_len = skb_len_func(skb); |

119 | vars->ldelay = now - skb_time_func(skb); |

120 | |

121 | if (unlikely(skb_len > stats->maxpacket)) |

122 | stats->maxpacket = skb_len; |

123 | |

124 | if (codel_time_before(vars->ldelay, params->target) || |

125 | *backlog <= params->mtu) { |

126 | /* went below - stay below for at least interval */ |

127 | vars->first_above_time = 0; |

128 | return false; |

129 | } |

130 | ok_to_drop = false; |

131 | if (vars->first_above_time == 0) { |

132 | /* just went above from below. If we stay above |

133 | * for at least interval we'll say it's ok to drop |

134 | */ |

135 | vars->first_above_time = now + params->interval; |

136 | } else if (codel_time_after(now, vars->first_above_time)) { |

137 | ok_to_drop = true; |

138 | } |

139 | return ok_to_drop; |

140 | } |

141 | |

142 | static struct sk_buff *codel_dequeue(void *ctx, |

143 | u32 *backlog, |

144 | struct codel_params *params, |

145 | struct codel_vars *vars, |

146 | struct codel_stats *stats, |

147 | codel_skb_len_t skb_len_func, |

148 | codel_skb_time_t skb_time_func, |

149 | codel_skb_drop_t drop_func, |

150 | codel_skb_dequeue_t dequeue_func) |

151 | { |

152 | struct sk_buff *skb = dequeue_func(vars, ctx); |

153 | codel_time_t now; |

154 | bool drop; |

155 | |

156 | if (!skb) { |

157 | vars->dropping = false; |

158 | return skb; |

159 | } |

160 | now = codel_get_time(); |

161 | drop = codel_should_drop(skb, ctx, vars, params, stats, |

162 | skb_len_func, skb_time_func, backlog, now); |

163 | if (vars->dropping) { |

164 | if (!drop) { |

165 | /* sojourn time below target - leave dropping state */ |

166 | vars->dropping = false; |

167 | } else if (codel_time_after_eq(now, vars->drop_next)) { |

168 | /* It's time for the next drop. Drop the current |

169 | * packet and dequeue the next. The dequeue might |

170 | * take us out of dropping state. |

171 | * If not, schedule the next drop. |

172 | * A large backlog might result in drop rates so high |

173 | * that the next drop should happen now, |

174 | * hence the while loop. |

175 | */ |

176 | while (vars->dropping && |

177 | codel_time_after_eq(now, vars->drop_next)) { |

178 | vars->count++; /* dont care of possible wrap |

179 | * since there is no more divide |

180 | */ |

181 | codel_Newton_step(vars); |

182 | if (params->ecn && INET_ECN_set_ce(skb)) { |

183 | stats->ecn_mark++; |

184 | vars->drop_next = |

185 | codel_control_law(vars->drop_next, |

186 | params->interval, |

187 | vars->rec_inv_sqrt); |

188 | goto end; |

189 | } |

190 | stats->drop_len += skb_len_func(skb); |

191 | drop_func(skb, ctx); |

192 | stats->drop_count++; |

193 | skb = dequeue_func(vars, ctx); |

194 | if (!codel_should_drop(skb, ctx, |

195 | vars, params, stats, |

196 | skb_len_func, |

197 | skb_time_func, |

198 | backlog, now)) { |

199 | /* leave dropping state */ |

200 | vars->dropping = false; |

201 | } else { |

202 | /* and schedule the next drop */ |

203 | vars->drop_next = |

204 | codel_control_law(vars->drop_next, |

205 | params->interval, |

206 | vars->rec_inv_sqrt); |

207 | } |

208 | } |

209 | } |

210 | } else if (drop) { |

211 | u32 delta; |

212 | |

213 | if (params->ecn && INET_ECN_set_ce(skb)) { |

214 | stats->ecn_mark++; |

215 | } else { |

216 | stats->drop_len += skb_len_func(skb); |

217 | drop_func(skb, ctx); |

218 | stats->drop_count++; |

219 | |

220 | skb = dequeue_func(vars, ctx); |

221 | drop = codel_should_drop(skb, ctx, vars, params, |

222 | stats, skb_len_func, |

223 | skb_time_func, backlog, now); |

224 | } |

225 | vars->dropping = true; |

226 | /* if min went above target close to when we last went below it |

227 | * assume that the drop rate that controlled the queue on the |

228 | * last cycle is a good starting point to control it now. |

229 | */ |

230 | delta = vars->count - vars->lastcount; |

231 | if (delta > 1 && |

232 | codel_time_before(now - vars->drop_next, |

233 | 16 * params->interval)) { |

234 | vars->count = delta; |

235 | /* we dont care if rec_inv_sqrt approximation |

236 | * is not very precise : |

237 | * Next Newton steps will correct it quadratically. |

238 | */ |

239 | codel_Newton_step(vars); |

240 | } else { |

241 | vars->count = 1; |

242 | vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT; |

243 | } |

244 | vars->lastcount = vars->count; |

245 | vars->drop_next = codel_control_law(now, params->interval, |

246 | vars->rec_inv_sqrt); |

247 | } |

248 | end: |

249 | if (skb && codel_time_after(vars->ldelay, params->ce_threshold) && |

250 | INET_ECN_set_ce(skb)) |

251 | stats->ce_mark++; |

252 | return skb; |

253 | } |

254 | |

255 | #endif |

256 |