src/peer_sourcehash.cc

   1 /*
   2  * Copyright (C) 1996-2022 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS files for details.
   7  */
   8
   9 /* DEBUG: section 39    Peer source hash based selection */
  10
  11 #include "squid.h"
  12 #include "CachePeer.h"
  13 #include "HttpRequest.h"
  14 #include "mgr/Registration.h"
  15 #include "neighbors.h"
  16 #include "peer_sourcehash.h"
  17 #include "PeerSelectState.h"
  18 #include "SquidConfig.h"
  19 #include "Store.h"
  20
  21 #include <cmath>
  22
  23 #define ROTATE_LEFT(x, n) (((x) << (n)) | ((x) >> (32-(n))))
  24
  25 static int n_sourcehash_peers = 0;
  26 static CachePeer **sourcehash_peers = nullptr;
  27 static OBJH peerSourceHashCachemgr;
  28 static void peerSourceHashRegisterWithCacheManager(void);
  29
  30 static int
  31 peerSortWeight(const void *a, const void *b)
  32 {
  33     const CachePeer *const *p1 = (const CachePeer *const *)a;
  34     const CachePeer *const *p2 = (const CachePeer *const *)b;
  35     return (*p1)->weight - (*p2)->weight;
  36 }
  37
  38 void
  39 peerSourceHashInit(void)
  40 {
  41     int W = 0;
  42     int K;
  43     int k;
  44     double P_last, X_last, Xn;
  45     CachePeer *p;
  46     CachePeer **P;
  47     char *t;
  48     /* Clean up */
  49
  50     for (k = 0; k < n_sourcehash_peers; ++k) {
  51         cbdataReferenceDone(sourcehash_peers[k]);
  52     }
  53
  54     safe_free(sourcehash_peers);
  55     n_sourcehash_peers = 0;
  56     /* find out which peers we have */
  57
  58     for (p = Config.peers; p; p = p->next) {
  59         if (!p->options.sourcehash)
  60             continue;
  61
  62         assert(p->type == PEER_PARENT);
  63
  64         if (p->weight == 0)
  65             continue;
  66
  67         ++n_sourcehash_peers;
  68
  69         W += p->weight;
  70     }
  71
  72     peerSourceHashRegisterWithCacheManager();
  73
  74     if (n_sourcehash_peers == 0)
  75         return;
  76
  77     sourcehash_peers = (CachePeer **)xcalloc(n_sourcehash_peers, sizeof(*sourcehash_peers));
  78
  79     /* Build a list of the found peers and calculate hashes and load factors */
  80     for (P = sourcehash_peers, p = Config.peers; p; p = p->next) {
  81         if (!p->options.sourcehash)
  82             continue;
  83
  84         if (p->weight == 0)
  85             continue;
  86
  87         /* calculate this peers hash */
  88         p->sourcehash.hash = 0;
  89
  90         for (t = p->name; *t != 0; ++t)
  91             p->sourcehash.hash += ROTATE_LEFT(p->sourcehash.hash, 19) + (unsigned int) *t;
  92
  93         p->sourcehash.hash += p->sourcehash.hash * 0x62531965;
  94
  95         p->sourcehash.hash = ROTATE_LEFT(p->sourcehash.hash, 21);
  96
  97         /* and load factor */
  98         p->sourcehash.load_factor = ((double) p->weight) / (double) W;
  99
 100         if (floor(p->sourcehash.load_factor * 1000.0) == 0.0)
 101             p->sourcehash.load_factor = 0.0;
 102
 103         /* add it to our list of peers */
 104         *P++ = cbdataReference(p);
 105     }
 106
 107     /* Sort our list on weight */
 108     qsort(sourcehash_peers, n_sourcehash_peers, sizeof(*sourcehash_peers), peerSortWeight);
 109
 110     /* Calculate the load factor multipliers X_k
 111      *
 112      * X_1 = pow ((K*p_1), (1/K))
 113      * X_k = ([K-k+1] * [P_k - P_{k-1}])/(X_1 * X_2 * ... * X_{k-1})
 114      * X_k += pow ((X_{k-1}, {K-k+1})
 115      * X_k = pow (X_k, {1/(K-k+1)})
 116      * simplified to have X_1 part of the loop
 117      */
 118     K = n_sourcehash_peers;
 119
 120     P_last = 0.0;       /* Empty P_0 */
 121
 122     Xn = 1.0;           /* Empty starting point of X_1 * X_2 * ... * X_{x-1} */
 123
 124     X_last = 0.0;       /* Empty X_0, nullifies the first pow statement */
 125
 126     for (k = 1; k <= K; ++k) {
 127         double Kk1 = (double) (K - k + 1);
 128         p = sourcehash_peers[k - 1];
 129         p->sourcehash.load_multiplier = (Kk1 * (p->sourcehash.load_factor - P_last)) / Xn;
 130         p->sourcehash.load_multiplier += pow(X_last, Kk1);
 131         p->sourcehash.load_multiplier = pow(p->sourcehash.load_multiplier, 1.0 / Kk1);
 132         Xn *= p->sourcehash.load_multiplier;
 133         X_last = p->sourcehash.load_multiplier;
 134         P_last = p->sourcehash.load_factor;
 135     }
 136 }
 137
 138 static void
 139 peerSourceHashRegisterWithCacheManager(void)
 140 {
 141     Mgr::RegisterAction("sourcehash", "peer sourcehash information",
 142                         peerSourceHashCachemgr, 0, 1);
 143 }
 144
 145 CachePeer *
 146 peerSourceHashSelectParent(PeerSelector *ps)
 147 {
 148     int k;
 149     const char *c;
 150     CachePeer *p = nullptr;
 151     CachePeer *tp;
 152     unsigned int user_hash = 0;
 153     unsigned int combined_hash;
 154     double score;
 155     double high_score = 0;
 156     const char *key = nullptr;
 157     char ntoabuf[MAX_IPSTRLEN];
 158
 159     if (n_sourcehash_peers == 0)
 160         return nullptr;
 161
 162     assert(ps);
 163     HttpRequest *request = ps->request;
 164
 165     key = request->client_addr.toStr(ntoabuf, sizeof(ntoabuf));
 166
 167     /* calculate hash key */
 168     debugs(39, 2, "peerSourceHashSelectParent: Calculating hash for " << key);
 169
 170     for (c = key; *c != 0; ++c)
 171         user_hash += ROTATE_LEFT(user_hash, 19) + *c;
 172
 173     /* select CachePeer */
 174     for (k = 0; k < n_sourcehash_peers; ++k) {
 175         tp = sourcehash_peers[k];
 176         combined_hash = (user_hash ^ tp->sourcehash.hash);
 177         combined_hash += combined_hash * 0x62531965;
 178         combined_hash = ROTATE_LEFT(combined_hash, 21);
 179         score = combined_hash * tp->sourcehash.load_multiplier;
 180         debugs(39, 3, "peerSourceHashSelectParent: " << tp->name << " combined_hash " << combined_hash  <<
 181                " score " << std::setprecision(0) << score);
 182
 183         if ((score > high_score) && peerHTTPOkay(tp, ps)) {
 184             p = tp;
 185             high_score = score;
 186         }
 187     }
 188
 189     if (p)
 190         debugs(39, 2, "peerSourceHashSelectParent: selected " << p->name);
 191
 192     return p;
 193 }
 194
 195 static void
 196 peerSourceHashCachemgr(StoreEntry * sentry)
 197 {
 198     CachePeer *p;
 199     int sumfetches = 0;
 200     storeAppendPrintf(sentry, "%24s %10s %10s %10s %10s\n",
 201                       "Hostname",
 202                       "Hash",
 203                       "Multiplier",
 204                       "Factor",
 205                       "Actual");
 206
 207     for (p = Config.peers; p; p = p->next)
 208         sumfetches += p->stats.fetches;
 209
 210     for (p = Config.peers; p; p = p->next) {
 211         storeAppendPrintf(sentry, "%24s %10x %10f %10f %10f\n",
 212                           p->name, p->sourcehash.hash,
 213                           p->sourcehash.load_multiplier,
 214                           p->sourcehash.load_factor,
 215                           sumfetches ? (double) p->stats.fetches / sumfetches : -1.0);
 216     }
 217 }
 218