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/*
* Copyright (c) 2021-2022 Cisco and/or its affiliates.
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <hicn/hicn-light/config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <hicn/core/strategy.h>
#include <hicn/core/strategy_vft.h>
#include <hicn/core/nexthops.h>
#include <hicn/core/fib_entry.h>
#include "load_balancer.h"
#define AVG_PI_THRESHOLD 1e-3
#define AVG_PI_MIN 0.1
#define ALPHA 0.9
/* Shorthand */
#define nexthop_state_t strategy_load_balancer_nexthop_state_t
#define nexthop_state(nexthops, i) (&nexthops->state[i].load_balancer)
static const nexthop_state_t NEXTHOP_STATE_INIT = {
.pi = 0,
.avg_pi = 0.0,
.weight = 1,
};
static inline void update_state(nexthop_state_t *state) {
state->avg_pi = (state->avg_pi * ALPHA) + (state->pi * 1 - ALPHA);
if (state->avg_pi < AVG_PI_THRESHOLD) state->avg_pi = AVG_PI_MIN;
state->weight = 1 / state->avg_pi;
}
static inline void update_state_inc(nexthop_state_t *state) {
state->pi++;
update_state(state);
}
static inline void update_state_dec(nexthop_state_t *state) {
if (state->pi > 0) state->pi--;
update_state(state);
}
static inline void reset_all(nexthops_t *nexthops) {
nexthops_enumerate(nexthops, i, nexthop, {
(void)nexthop;
nexthops->state[i].load_balancer = NEXTHOP_STATE_INIT;
});
}
static int strategy_load_balancer_initialize(strategy_entry_t *entry,
const void *forwarder) {
/* No reset, this will be done when a nexthop is added */
entry->forwarder = forwarder;
return 0;
}
static int strategy_load_balancer_finalize(strategy_entry_t *entry) {
/* Nothing to do */
return 0;
}
static int strategy_load_balancer_add_nexthop(strategy_entry_t *entry,
nexthops_t *nexthops,
off_t offset) {
/* We reset the state of all nexthops */
reset_all(nexthops);
return 0;
}
static int strategy_load_balancer_remove_nexthop(strategy_entry_t *entry,
nexthops_t *nexthops,
off_t offset) {
reset_all(nexthops);
return 0;
}
static nexthops_t *strategy_load_balancer_lookup_nexthops(
strategy_entry_t *entry, nexthops_t *nexthops, const msgbuf_t *msgbuf) {
if (nexthops_get_curlen(nexthops) == 0) return nexthops;
/* Compute the sum of weights of potential next hops */
double sum = 0;
nexthops_enumerate(nexthops, i, nexthop, {
(void)nexthop;
sum += nexthops_state(nexthops, i).load_balancer.weight;
});
/* Perform weighted random selection */
double distance = (double)rand() * sum / ((double)RAND_MAX + 1);
nexthops_enumerate(nexthops, i, nexthop, {
distance -= nexthop_state(nexthops, i)->weight;
if (distance < 0) {
nexthops_select(nexthops, i);
update_state_inc(nexthop_state(nexthops, i));
break;
}
});
return nexthops;
}
static int strategy_load_balancer_on_timeout(
strategy_entry_t *entry, nexthops_t *nexthops,
const nexthops_t *timeout_nexthops) {
/*
* As we have few nexthops in FIB entry, and even fewer selected ones in
* nexthops, we can allow for linear search that will be very efficient
* CPU-wise.
*/
nexthops_foreach(timeout_nexthops, timeout_nexthop, {
nexthops_enumerate(nexthops, i, nexthop, {
if (nexthop == timeout_nexthop)
update_state_dec(nexthop_state(nexthops, i));
});
});
return 0;
}
static int strategy_load_balancer_on_data(strategy_entry_t *entry,
nexthops_t *nexthops,
const nexthops_t *data_nexthops,
const msgbuf_t *msgbuf,
Ticks pitEntryCreation,
Ticks objReception) {
return strategy_load_balancer_on_timeout(entry, nexthops, data_nexthops);
}
#undef nexthop_state_t
DECLARE_STRATEGY(load_balancer);
#undef nexthop_state_t
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