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Clock.c
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Clock.c
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//
// Clock, the same as FIFO-Reinsertion or second chance, is a FIFO with
// which inserts back some objects upon eviction
//
//
// Clock.c
// libCacheSim
//
// Created by Juncheng on 12/4/18.
// Copyright © 2018 Juncheng. All rights reserved.
//
#include "../../dataStructure/hashtable/hashtable.h"
#include "../../include/libCacheSim/evictionAlgo.h"
#ifdef __cplusplus
extern "C" {
#endif
// #define USE_BELADY
#undef USE_BELADY
static const char *DEFAULT_PARAMS = "n-bit-counter=1";
// ***********************************************************************
// **** ****
// **** function declarations ****
// **** ****
// ***********************************************************************
static void Clock_parse_params(cache_t *cache,
const char *cache_specific_params);
static void Clock_free(cache_t *cache);
static bool Clock_get(cache_t *cache, const request_t *req);
static cache_obj_t *Clock_find(cache_t *cache, const request_t *req,
const bool update_cache);
static cache_obj_t *Clock_insert(cache_t *cache, const request_t *req);
static cache_obj_t *Clock_to_evict(cache_t *cache, const request_t *req);
static void Clock_evict(cache_t *cache, const request_t *req);
static bool Clock_remove(cache_t *cache, const obj_id_t obj_id);
// ***********************************************************************
// **** ****
// **** end user facing functions ****
// **** ****
// ***********************************************************************
/**
* @brief initialize a Clock cache
*
* @param ccache_params some common cache parameters
* @param cache_specific_params Clock specific parameters as a string
*/
cache_t *Clock_init(const common_cache_params_t ccache_params,
const char *cache_specific_params) {
cache_t *cache = cache_struct_init("Clock", ccache_params, cache_specific_params);
cache->cache_init = Clock_init;
cache->cache_free = Clock_free;
cache->get = Clock_get;
cache->find = Clock_find;
cache->insert = Clock_insert;
cache->evict = Clock_evict;
cache->remove = Clock_remove;
cache->can_insert = cache_can_insert_default;
cache->get_n_obj = cache_get_n_obj_default;
cache->get_occupied_byte = cache_get_occupied_byte_default;
cache->to_evict = Clock_to_evict;
cache->obj_md_size = 0;
#ifdef USE_BELADY
snprintf(cache->cache_name, CACHE_NAME_ARRAY_LEN, "Clock_Belady");
#endif
cache->eviction_params = malloc(sizeof(Clock_params_t));
memset(cache->eviction_params, 0, sizeof(Clock_params_t));
Clock_params_t *params = (Clock_params_t *)cache->eviction_params;
params->q_head = NULL;
params->q_tail = NULL;
params->n_bit_counter = 1;
params->max_freq = 1;
Clock_parse_params(cache, DEFAULT_PARAMS);
if (cache_specific_params != NULL) {
Clock_parse_params(cache, cache_specific_params);
}
if (params->n_bit_counter != 1) {
snprintf(cache->cache_name, CACHE_NAME_ARRAY_LEN, "Clock-%d",
params->n_bit_counter);
}
return cache;
}
/**
* free resources used by this cache
*
* @param cache
*/
static void Clock_free(cache_t *cache) {
free(cache->eviction_params);
cache_struct_free(cache);
}
/**
* @brief this function is the user facing API
* it performs the following logic
*
* ```
* if obj in cache:
* update_metadata
* return true
* else:
* if cache does not have enough space:
* evict until it has space to insert
* insert the object
* return false
* ```
*
* @param cache
* @param req
* @return true if cache hit, false if cache miss
*/
static bool Clock_get(cache_t *cache, const request_t *req) {
return cache_get_base(cache, req);
}
// ***********************************************************************
// **** ****
// **** developer facing APIs (used by cache developer) ****
// **** ****
// ***********************************************************************
/**
* @brief check whether an object is in the cache
*
* @param cache
* @param req
* @param update_cache whether to update the cache,
* if true, the object is promoted
* and if the object is expired, it is removed from the cache
* @return true on hit, false on miss
*/
static cache_obj_t *Clock_find(cache_t *cache, const request_t *req,
const bool update_cache) {
Clock_params_t *params = (Clock_params_t *)cache->eviction_params;
cache_obj_t *obj = cache_find_base(cache, req, update_cache);
if (obj != NULL && update_cache) {
if (obj->clock.freq < params->max_freq) {
obj->clock.freq += 1;
}
#ifdef USE_BELADY
obj->next_access_vtime = req->next_access_vtime;
#endif
}
return obj;
}
/**
* @brief insert an object into the cache,
* update the hash table and cache metadata
* this function assumes the cache has enough space
* and eviction is not part of this function
*
* @param cache
* @param req
* @return the inserted object
*/
static cache_obj_t *Clock_insert(cache_t *cache, const request_t *req) {
Clock_params_t *params = (Clock_params_t *)cache->eviction_params;
cache_obj_t *obj = cache_insert_base(cache, req);
prepend_obj_to_head(¶ms->q_head, ¶ms->q_tail, obj);
obj->clock.freq = 0;
#ifdef USE_BELADY
obj->next_access_vtime = req->next_access_vtime;
#endif
return obj;
}
/**
* @brief find the object to be evicted
* this function does not actually evict the object or update metadata
* not all eviction algorithms support this function
* because the eviction logic cannot be decoupled from finding eviction
* candidate, so use assert(false) if you cannot support this function
*
* @param cache the cache
* @return the object to be evicted
*/
static cache_obj_t *Clock_to_evict(cache_t *cache, const request_t *req) {
Clock_params_t *params = (Clock_params_t *)cache->eviction_params;
int n_round = 0;
cache_obj_t *obj_to_evict = params->q_tail;
#ifdef USE_BELADY
while (obj_to_evict->next_access_vtime != INT64_MAX) {
#else
while (obj_to_evict->clock.freq - n_round >= 1) {
#endif
obj_to_evict = obj_to_evict->queue.prev;
if (obj_to_evict == NULL) {
obj_to_evict = params->q_tail;
n_round += 1;
}
}
return obj_to_evict;
}
/**
* @brief evict an object from the cache
* it needs to call cache_evict_base before returning
* which updates some metadata such as n_obj, occupied size, and hash table
*
* @param cache
* @param req not used
* @param evicted_obj if not NULL, return the evicted object to caller
*/
static void Clock_evict(cache_t *cache, const request_t *req) {
Clock_params_t *params = (Clock_params_t *)cache->eviction_params;
cache_obj_t *obj_to_evict = params->q_tail;
while (obj_to_evict->clock.freq >= 1) {
obj_to_evict->clock.freq -= 1;
params->n_obj_rewritten += 1;
params->n_byte_rewritten += obj_to_evict->obj_size;
move_obj_to_head(¶ms->q_head, ¶ms->q_tail, obj_to_evict);
obj_to_evict = params->q_tail;
}
remove_obj_from_list(¶ms->q_head, ¶ms->q_tail, obj_to_evict);
cache_evict_base(cache, obj_to_evict, true);
}
/**
* @brief remove the given object from the cache
* note that eviction should not call this function, but rather call
* `cache_evict_base` because we track extra metadata during eviction
*
* and this function is different from eviction
* because it is used to for user trigger
* remove, and eviction is used by the cache to make space for new objects
*
* it needs to call cache_remove_obj_base before returning
* which updates some metadata such as n_obj, occupied size, and hash table
*
* @param cache
* @param obj
*/
static void Clock_remove_obj(cache_t *cache, cache_obj_t *obj) {
Clock_params_t *params = (Clock_params_t *)cache->eviction_params;
DEBUG_ASSERT(obj != NULL);
remove_obj_from_list(¶ms->q_head, ¶ms->q_tail, obj);
cache_remove_obj_base(cache, obj, true);
}
/**
* @brief remove an object from the cache
* this is different from cache_evict because it is used to for user trigger
* remove, and eviction is used by the cache to make space for new objects
*
* it needs to call cache_remove_obj_base before returning
* which updates some metadata such as n_obj, occupied size, and hash table
*
* @param cache
* @param obj_id
* @return true if the object is removed, false if the object is not in the
* cache
*/
static bool Clock_remove(cache_t *cache, const obj_id_t obj_id) {
cache_obj_t *obj = hashtable_find_obj_id(cache->hashtable, obj_id);
if (obj == NULL) {
return false;
}
Clock_remove_obj(cache, obj);
return true;
}
// ***********************************************************************
// **** ****
// **** parameter set up functions ****
// **** ****
// ***********************************************************************
static const char *Clock_current_params(cache_t *cache,
Clock_params_t *params) {
static __thread char params_str[128];
int n =
snprintf(params_str, 128, "n-bit-counter=%d\n", params->n_bit_counter);
return params_str;
}
static void Clock_parse_params(cache_t *cache,
const char *cache_specific_params) {
Clock_params_t *params = (Clock_params_t *)cache->eviction_params;
char *params_str = strdup(cache_specific_params);
char *old_params_str = params_str;
char *end;
while (params_str != NULL && params_str[0] != '\0') {
/* different parameters are separated by comma,
* key and value are separated by = */
char *key = strsep((char **)¶ms_str, "=");
char *value = strsep((char **)¶ms_str, ",");
// skip the white space
while (params_str != NULL && *params_str == ' ') {
params_str++;
}
if (strcasecmp(key, "n-bit-counter") == 0) {
params->n_bit_counter = (int)strtol(value, &end, 0);
params->max_freq = (1 << params->n_bit_counter) - 1;
if (strlen(end) > 2) {
ERROR("param parsing error, find string \"%s\" after number\n", end);
}
} else if (strcasecmp(key, "print") == 0) {
printf("current parameters: %s\n", Clock_current_params(cache, params));
exit(0);
} else {
ERROR("%s does not have parameter %s, example paramters %s\n",
cache->cache_name, key, Clock_current_params(cache, params));
exit(1);
}
}
free(old_params_str);
}
#ifdef __cplusplus
}
#endif