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b698f0f4a2
Now we can compute the max place depending on the number of servers, maximum weight and weight scale. The formula has been stored as a comment so that it's easy to choose between smooth weight ramp up and high number of servers. The default scale has been set to 16, which permits 4000 servers with a granularity of 6% in the worst case (weight=1).
400 lines
9.5 KiB
C
400 lines
9.5 KiB
C
/*
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* experimental weighted round robin scheduler - (c) 2007 willy tarreau.
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*
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* This filling algorithm is excellent at spreading the servers, as it also
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* takes care of keeping the most uniform distance between occurences of each
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* server, by maximizing this distance. It reduces the number of variables
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* and expensive operations.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include "eb32tree.h"
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struct srv {
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struct eb32_node node;
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struct eb_root *tree; // we want to know where the server is
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int num;
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int w; /* weight */
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int next, last;
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int rem;
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} *srv;
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/* those trees represent a sliding window of 3 time frames */
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struct eb_root tree_0 = EB_ROOT;
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struct eb_root tree_1 = EB_ROOT;
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struct eb_root tree_2 = EB_ROOT;
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struct eb_root *init_tree; /* receives positions 0..sw-1 */
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struct eb_root *next_tree; /* receives positions >= 2sw */
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int nsrv; /* # of servers */
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int nsw, sw; /* sum of weights */
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int p; /* current position, between sw..2sw-1 */
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/* queue a server in the weights tree */
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void queue_by_weight(struct eb_root *root, struct srv *s) {
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s->node.key = 255 - s->w;
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eb32_insert(root, &s->node);
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s->tree = root;
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}
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/* queue a server in the weight tree <root>, except if its weight is 0 */
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void queue_by_weight_0(struct eb_root *root, struct srv *s) {
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if (s->w) {
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s->node.key = 255 - s->w;
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eb32_insert(root, &s->node);
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s->tree = root;
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} else {
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s->tree = NULL;
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}
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}
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static inline void dequeue_srv(struct srv *s) {
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eb32_delete(&s->node);
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}
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/* queues a server into the correct tree depending on ->next */
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void put_srv(struct srv *s) {
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if (s->w <= 0 ||
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s->next >= 2*sw || /* delay everything which does not fit into the window */
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s->next >= sw+nsw) { /* and everything which does not fit into the theorical new window */
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/* put into next tree */
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s->next -= sw; // readjust next in case we could finally take this back to current.
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queue_by_weight_0(next_tree, s);
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} else {
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// The overflow problem is caused by the scale we want to apply to user weight
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// to turn it into effective weight. Since this is only used to provide a smooth
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// slowstart on very low weights (1), it is a pure waste. Thus, we just have to
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// apply a small scaling factor and warn the user that slowstart is not very smooth
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// on low weights.
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// The max key is about ((scale*maxw)*(scale*maxw)*nbsrv)/ratio (where the ratio is
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// the arbitrary divide we perform in the examples above). Assuming that ratio==scale,
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// this translates to maxkey=scale*maxw^2*nbsrv, so
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// max_nbsrv=2^32/255^2/scale ~= 66051/scale
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// Using a scale of 16 is enough to support 4000 servers without overflow, providing
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// 6% steps during slowstart.
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s->node.key = 256 * s->next + (16*255 + s->rem - s->w) / 16;
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/* check for overflows */
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if ((int)s->node.key < 0)
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printf(" OV: srv=%p w=%d rem=%d next=%d key=%d", s, s->w, s->rem, s->next, s->node.key);
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eb32_insert(&tree_0, &s->node);
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s->tree = &tree_0;
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}
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}
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/* prepares a server when extracting it from the init tree */
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static inline void get_srv_init(struct srv *s) {
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s->next = s->rem = 0;
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}
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/* prepares a server when extracting it from the next tree */
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static inline void get_srv_next(struct srv *s) {
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s->next += sw;
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}
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/* prepares a server when extracting it from the next tree */
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static inline void get_srv_down(struct srv *s) {
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s->next = p;
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}
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/* prepares a server when extracting it from its tree */
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void get_srv(struct srv *s) {
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if (s->tree == init_tree) {
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get_srv_init(s);
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}
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else if (s->tree == next_tree) {
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get_srv_next(s);
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}
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else if (s->tree == NULL) {
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get_srv_down(s);
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}
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}
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/* return next server from the current tree, or a server from the init tree
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* if appropriate. If both trees are empty, return NULL.
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*/
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struct srv *get_next_server() {
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struct eb32_node *node;
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struct srv *s;
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node = eb32_first(&tree_0);
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s = eb32_entry(node, struct srv, node);
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if (!node || s->next > p) {
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/* either we have no server left, or we have a hole */
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struct eb32_node *node2;
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node2 = eb32_first(init_tree);
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if (node2) {
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node = node2;
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s = eb32_entry(node, struct srv, node);
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get_srv_init(s);
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if (s->w == 0)
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node = NULL;
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s->node.key = 0; // do not display random values
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}
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}
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if (node)
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return s;
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else
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return NULL;
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}
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void update_position(struct srv *s) {
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//if (s->tree == init_tree) {
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if (!s->next) {
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// first time ever for this server
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s->last = p;
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s->next = p + nsw / s->w;
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s->rem += nsw % s->w;
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if (s->rem >= s->w) {
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s->rem -= s->w;
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s->next++;
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}
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} else {
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s->last = s->next; // or p ?
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//s->next += sw / s->w;
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//s->rem += sw % s->w;
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s->next += nsw / s->w;
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s->rem += nsw % s->w;
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if (s->rem >= s->w) {
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s->rem -= s->w;
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s->next++;
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}
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}
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}
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/* switches trees init_tree and next_tree. init_tree should be empty when
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* this happens, and next_tree filled with servers sorted by weights.
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*/
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void switch_trees() {
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struct eb_root *swap;
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swap = init_tree;
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init_tree = next_tree;
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next_tree = swap;
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sw = nsw;
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p = sw;
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}
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main(int argc, char **argv) {
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int conns;
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int i;
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struct srv *s;
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argc--; argv++;
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nsrv = argc;
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if (!nsrv)
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exit(1);
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srv = (struct srv *)calloc(nsrv, sizeof(struct srv));
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sw = 0;
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for (i = 0; i < nsrv; i++) {
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s = &srv[i];
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s->num = i;
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s->w = atol(argv[i]);
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sw += s->w;
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}
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nsw = sw;
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init_tree = &tree_1;
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next_tree = &tree_2;
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/* and insert all the servers in the PREV tree */
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/* note that it is required to insert them according to
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* the reverse order of their weights.
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*/
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printf("---------------:");
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for (i = 0; i < nsrv; i++) {
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s = &srv[i];
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queue_by_weight_0(init_tree, s);
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printf("%2d", s->w);
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}
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printf("\n");
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p = sw; // time base of current tree
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conns = 0;
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while (1) {
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struct eb32_node *node;
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printf("%08d|%06d: ", conns, p);
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/* if we have en empty tree, let's first try to collect weights
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* which might have changed.
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*/
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if (!sw) {
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if (nsw) {
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sw = nsw;
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p = sw;
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/* do not switch trees, otherwise new servers (from init)
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* would end up in next.
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*/
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//switch_trees();
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//printf("bla\n");
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}
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else
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goto next_iteration;
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}
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s = get_next_server();
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if (!s) {
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printf("----------- switch (empty) -- sw=%d -> %d ---------\n", sw, nsw);
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switch_trees();
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s = get_next_server();
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printf("%08d|%06d: ", conns, p);
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if (!s)
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goto next_iteration;
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}
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else if (s->next >= 2*sw) {
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printf("ARGGGGG! s[%d].next=%d, max=%d\n", s->num, s->next, 2*sw-1);
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}
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/* now we have THE server we want to put at this position */
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for (i = 0; i < s->num; i++) {
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if (srv[i].w > 0)
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printf(". ");
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else
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printf("_ ");
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}
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printf("# ");
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for (i = s->num + 1; i < nsrv; i++) {
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if (srv[i].w > 0)
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printf(". ");
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else
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printf("_ ");
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}
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printf(" : ");
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printf("s=%02d v=%04d w=%03d n=%03d r=%03d ",
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s->num, s->node.key, s->w, s->next, s->rem);
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update_position(s);
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printf(" | next=%03d, rem=%03d ", s->next, s->rem);
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if (s->next >= sw * 2) {
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dequeue_srv(s);
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//queue_by_weight(next_tree, s);
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put_srv(s);
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printf(" => next (w=%d, n=%d) ", s->w, s->next);
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}
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else {
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printf(" => curr ");
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//s->node.key = s->next;
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/* we want to ensure that in case of conflicts, servers with
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* the highest weights will get served first. Also, we still
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* have the remainder to see where the entry expected to be
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* inserted.
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*/
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//s->node.key = 256 * s->next + 255 - s->w;
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//s->node.key = sw * s->next + sw / s->w;
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//s->node.key = sw * s->next + s->rem; /// seems best (check with filltab15) !
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//s->node.key = (2 * sw * s->next) + s->rem + sw / s->w;
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/* FIXME: must be optimized */
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dequeue_srv(s);
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put_srv(s);
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//eb32i_insert(&tree_0, &s->node);
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//s->tree = &tree_0;
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}
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next_iteration:
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p++;
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conns++;
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if (/*conns == 30*/ /**/random()%100 == 0/**/) {
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int w = /*20*//**/random()%4096/**/;
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int num = /*1*//**/random()%nsrv/**/;
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struct srv *s = &srv[num];
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nsw = nsw - s->w + w;
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//sw=nsw;
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if (s->tree == init_tree) {
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printf(" -- chgwght1(%d): %d->%d, n=%d --", s->num, s->w, w, s->next);
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printf("(init)");
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s->w = w;
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dequeue_srv(s);
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queue_by_weight_0(s->tree, s);
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}
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else if (s->tree == NULL) {
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printf(" -- chgwght2(%d): %d->%d, n=%d --", s->num, s->w, w, s->next);
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printf("(down)");
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s->w = w;
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dequeue_srv(s);
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//queue_by_weight_0(init_tree, s);
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get_srv(s);
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s->next = p + (nsw + sw - p) / s->w;
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put_srv(s);
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}
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else {
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int oldnext;
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/* the server is either active or in the next queue */
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get_srv(s);
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printf(" -- chgwght3(%d): %d->%d, n=%d, sw=%d, nsw=%d --", s->num, s->w, w, s->next, sw, nsw);
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oldnext = s->next;
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s->w = w;
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/* we must measure how far we are from the end of the current window
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* and try to fit their as many entries as should theorically be.
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*/
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//s->w = s->w * (2*sw - p) / sw;
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if (s->w > 0) {
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int step = (nsw /*+ sw - p*/) / s->w;
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s->next = s->last + step;
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s->rem = 0;
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if (s->next > oldnext) {
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s->next = oldnext;
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printf(" aaaaaaa ");
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}
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if (s->next < p + 2) {
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s->next = p + step;
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printf(" bbbbbb ");
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}
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} else {
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printf(" push -- ");
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/* push it into the next tree */
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s->w = 0;
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s->next = p + sw;
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}
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dequeue_srv(s);
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printf(" n=%d", s->next);
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put_srv(s);
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}
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}
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printf("\n");
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if (0 && conns % 50000 == 0) {
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printf("-------- %-5d : changing all weights ----\n", conns);
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for (i = 0; i < nsrv; i++) {
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int w = i + 1;
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s = &srv[i];
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nsw = nsw - s->w + w;
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s->w = w;
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dequeue_srv(s);
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queue_by_weight_0(next_tree, s); // or init_tree ?
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}
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}
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}
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}
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