@@ -29,6 +29,14 @@ static uint64_t dmisses;
static uint64_t imem_accesses;
static uint64_t imisses;
+enum EvictionPolicy {
+ LRU,
+ FIFO,
+ RAND,
+};
+
+enum EvictionPolicy policy;
+
/*
* A CacheSet is a set of cache blocks. A memory block that maps to a set can be
* put in any of the blocks inside the set. The number of block per set is
@@ -48,6 +56,8 @@ static uint64_t imisses;
* The set number is used to identify the set in which the block may exist.
* The tag is compared against all the tags of a set to search for a match. If a
* match is found, then the access is a hit.
+ *
+ * The CacheSet also contains bookkeaping information about eviction details.
*/
typedef struct {
@@ -57,6 +67,9 @@ typedef struct {
typedef struct {
CacheBlock *blocks;
+ uint64_t *lru_priorities;
+ uint64_t lru_gen_counter;
+ GQueue *fifo_queue;
} CacheSet;
typedef struct {
@@ -77,6 +90,12 @@ typedef struct {
uint64_t imisses;
} InsnData;
+void (*update_hit)(Cache *cache, int set, int blk);
+void (*update_miss)(Cache *cache, int set, int blk);
+
+void (*metadata_init)(Cache *cache);
+void (*metadata_destroy)(Cache *cache);
+
Cache *dcache, *icache;
static int pow_of_two(int num)
@@ -89,6 +108,103 @@ static int pow_of_two(int num)
return ret;
}
+/*
+ * LRU evection policy: For each set, a generation counter is maintained
+ * alongside a priority array.
+ *
+ * On each set access, the generation counter is incremented.
+ *
+ * On a cache hit: The hit-block is assigned the current generation counter,
+ * indicating that it is the most recently used block.
+ *
+ * On a cache miss: The block with the least priority is searched and replaced
+ * with the newly-cached block, of which the priority is set to the current
+ * generation number.
+ */
+
+static void lru_priorities_init(Cache *cache)
+{
+ int i;
+
+ for (i = 0; i < cache->num_sets; i++) {
+ cache->sets[i].lru_priorities = g_new0(uint64_t, cache->assoc);
+ cache->sets[i].lru_gen_counter = 0;
+ }
+}
+
+static void lru_update_blk(Cache *cache, int set_idx, int blk_idx)
+{
+ CacheSet *set = &cache->sets[set_idx];
+ set->lru_priorities[blk_idx] = cache->sets[set_idx].lru_gen_counter;
+ set->lru_gen_counter++;
+}
+
+static int lru_get_lru_block(Cache *cache, int set_idx)
+{
+ int i, min_idx, min_priority;
+
+ min_priority = cache->sets[set_idx].lru_priorities[0];
+ min_idx = 0;
+
+ for (i = 1; i < cache->assoc; i++) {
+ if (cache->sets[set_idx].lru_priorities[i] < min_priority) {
+ min_priority = cache->sets[set_idx].lru_priorities[i];
+ min_idx = i;
+ }
+ }
+ return min_idx;
+}
+
+static void lru_priorities_destroy(Cache *cache)
+{
+ int i;
+
+ for (i = 0; i < cache->num_sets; i++) {
+ g_free(cache->sets[i].lru_priorities);
+ }
+}
+
+/*
+ * FIFO eviction policy: a FIFO queue is maintained for each CacheSet that
+ * stores accesses to the cache.
+ *
+ * On a compulsory miss: The block index is enqueued to the fifo_queue to
+ * indicate that it's the latest cached block.
+ *
+ * On a conflict miss: The first-in block is removed from the cache and the new
+ * block is put in its place and enqueued to the FIFO queue.
+ */
+
+static void fifo_init(Cache *cache)
+{
+ int i;
+
+ for (i = 0; i < cache->num_sets; i++) {
+ cache->sets[i].fifo_queue = g_queue_new();
+ }
+}
+
+static int fifo_get_first_block(Cache *cache, int set)
+{
+ GQueue *q = cache->sets[set].fifo_queue;
+ return GPOINTER_TO_INT(g_queue_pop_tail(q));
+}
+
+static void fifo_update_on_miss(Cache *cache, int set, int blk_idx)
+{
+ GQueue *q = cache->sets[set].fifo_queue;
+ g_queue_push_head(q, GINT_TO_POINTER(blk_idx));
+}
+
+static void fifo_destroy(Cache *cache)
+{
+ int i;
+
+ for (i = 0; i < cache->assoc; i++) {
+ g_queue_free(cache->sets[i].fifo_queue);
+ }
+}
+
static inline uint64_t extract_tag(Cache *cache, uint64_t addr)
{
return addr & cache->tag_mask;
@@ -139,6 +255,11 @@ static Cache *cache_init(int blksize, int assoc, int cachesize)
blk_mask = blksize - 1;
cache->set_mask = ((cache->num_sets - 1) << cache->blksize_shift);
cache->tag_mask = ~(cache->set_mask | blk_mask);
+
+ if (metadata_init) {
+ metadata_init(cache);
+ }
+
return cache;
}
@@ -155,12 +276,21 @@ static int get_invalid_block(Cache *cache, uint64_t set)
return -1;
}
-static int get_replaced_block(Cache *cache)
+static int get_replaced_block(Cache *cache, int set)
{
- return g_rand_int_range(rng, 0, cache->assoc);
+ switch (policy) {
+ case RAND:
+ return g_rand_int_range(rng, 0, cache->assoc);
+ case LRU:
+ return lru_get_lru_block(cache, set);
+ case FIFO:
+ return fifo_get_first_block(cache, set);
+ default:
+ g_assert_not_reached();
+ }
}
-static bool in_cache(Cache *cache, uint64_t addr)
+static int in_cache(Cache *cache, uint64_t addr)
{
int i;
uint64_t tag, set;
@@ -171,11 +301,11 @@ static bool in_cache(Cache *cache, uint64_t addr)
for (i = 0; i < cache->assoc; i++) {
if (cache->sets[set].blocks[i].tag == tag &&
cache->sets[set].blocks[i].valid) {
- return true;
+ return i;
}
}
- return false;
+ return -1;
}
/**
@@ -188,20 +318,28 @@ static bool in_cache(Cache *cache, uint64_t addr)
*/
static bool access_cache(Cache *cache, uint64_t addr)
{
+ int hit_blk, replaced_blk;
uint64_t tag, set;
- int replaced_blk;
-
- if (in_cache(cache, addr)) {
- return true;
- }
tag = extract_tag(cache, addr);
set = extract_set(cache, addr);
+ hit_blk = in_cache(cache, addr);
+ if (hit_blk != -1) {
+ if (update_hit) {
+ update_hit(cache, set, hit_blk);
+ }
+ return true;
+ }
+
replaced_blk = get_invalid_block(cache, set);
if (replaced_blk == -1) {
- replaced_blk = get_replaced_block(cache);
+ replaced_blk = get_replaced_block(cache, set);
+ }
+
+ if (update_miss) {
+ update_miss(cache, set, replaced_blk);
}
cache->sets[set].blocks[replaced_blk].tag = tag;
@@ -308,6 +446,10 @@ static void cache_free(Cache *cache)
g_free(cache->sets[i].blocks);
}
+ if (metadata_destroy) {
+ metadata_destroy(cache);
+ }
+
g_free(cache->sets);
g_free(cache);
}
@@ -395,6 +537,28 @@ static void plugin_exit(qemu_plugin_id_t id, void *p)
g_hash_table_destroy(miss_ht);
}
+static void policy_init()
+{
+ switch (policy) {
+ case LRU:
+ update_hit = lru_update_blk;
+ update_miss = lru_update_blk;
+ metadata_init = lru_priorities_init;
+ metadata_destroy = lru_priorities_destroy;
+ break;
+ case FIFO:
+ update_miss = fifo_update_on_miss;
+ metadata_init = fifo_init;
+ metadata_destroy = fifo_destroy;
+ break;
+ case RAND:
+ rng = g_rand_new();
+ break;
+ default:
+ g_assert_not_reached();
+ }
+}
+
QEMU_PLUGIN_EXPORT
int qemu_plugin_install(qemu_plugin_id_t id, const qemu_info_t *info,
int argc, char **argv)
@@ -414,6 +578,7 @@ int qemu_plugin_install(qemu_plugin_id_t id, const qemu_info_t *info,
iblksize = 64;
icachesize = iblksize * iassoc * 32;
+ policy = LRU;
for (i = 0; i < argc; i++) {
char *opt = argv[i];
@@ -431,12 +596,26 @@ int qemu_plugin_install(qemu_plugin_id_t id, const qemu_info_t *info,
dcachesize = g_ascii_strtoll(opt + 11, NULL, 10);
} else if (g_str_has_prefix(opt, "limit=")) {
limit = g_ascii_strtoll(opt + 6, NULL, 10);
+ } else if (g_str_has_prefix(opt, "evict=")) {
+ gchar *p = opt + 6;
+ if (g_strcmp0(p, "rand") == 0) {
+ policy = RAND;
+ } else if (g_strcmp0(p, "lru") == 0) {
+ policy = LRU;
+ } else if (g_strcmp0(p, "fifo") == 0) {
+ policy = FIFO;
+ } else {
+ fprintf(stderr, "invalid eviction policy: %s\n", opt);
+ return -1;
+ }
} else {
fprintf(stderr, "option parsing failed: %s\n", opt);
return -1;
}
}
+ policy_init();
+
dcache = cache_init(dblksize, dassoc, dcachesize);
if (!dcache) {
const char *err = cache_config_error(dblksize, dassoc, dcachesize);
@@ -453,8 +632,6 @@ int qemu_plugin_install(qemu_plugin_id_t id, const qemu_info_t *info,
return -1;
}
- rng = g_rand_new();
-
qemu_plugin_register_vcpu_tb_trans_cb(id, vcpu_tb_trans);
qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);