Implemented FIFO and LRU eviction policies.
Now one of the three eviction policies can be chosen as an argument. On
not specifying an argument, LRU is used by default.
Signed-off-by: Mahmoud Mandour <ma.mando...@gmail.com>
---
contrib/plugins/cache.c | 205 +++++++++++++++++++++++++++++++++++++---
1 file changed, 192 insertions(+), 13 deletions(-)
diff --git a/contrib/plugins/cache.c b/contrib/plugins/cache.c
index d8e8c750b6..be817da5b6 100644
--- a/contrib/plugins/cache.c
+++ b/contrib/plugins/cache.c
@@ -34,6 +34,14 @@ 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
@@ -53,6 +61,8 @@ 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.
*/
struct CacheBlock {
@@ -62,6 +72,9 @@ struct CacheBlock {
struct CacheSet {
struct CacheBlock *blocks;
+ uint64_t *lru_priorities;
+ uint64_t lru_gen_counter;
+ GQueue *fifo_queue;
};
struct Cache {
@@ -82,6 +95,12 @@ struct InsnData {
uint64_t imisses;
};
+void (*update_hit)(struct Cache *cache, int set, int blk);
+void (*update_miss)(struct Cache *cache, int set, int blk);
+
+void (*metadata_init)(struct Cache *cache);
+void (*metadata_destroy)(struct Cache *cache);
+
struct Cache *dcache, *icache;
static int pow_of_two(int num)
@@ -104,6 +123,103 @@ static inline uint64_t extract_set(struct Cache *cache,
uint64_t addr)
return (addr & cache->set_mask) >> cache->blksize_shift;
}
+/*
+ * 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(struct Cache *cache)
+{
+ int i, assoc;
+
+ assoc = cache->assoc;
+ for (i = 0; i < cache->num_sets; i++) {
+ cache->sets[i].lru_priorities = g_new0(uint64_t, assoc);
+ }
+}
+
+static void lru_update_blk(struct Cache *cache, int set_idx, int blk_idx)
+{
+ struct 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(struct 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(struct 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(struct 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(struct 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(struct 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(struct Cache *cache)
+{
+ int i;
+
+ for (i = 0; i < cache->assoc; i++) {
+ g_queue_free(cache->sets[i].fifo_queue);
+ }
+}
+
static bool bad_cache_params(int blksize, int assoc, int cachesize)
{
return (cachesize % blksize) != 0 || (cachesize % (blksize * assoc) != 0);
@@ -128,11 +244,17 @@ static struct Cache *cache_init(int blksize, int assoc,
int cachesize)
for (i = 0; i < cache->num_sets; i++) {
cache->sets[i].blocks = g_new0(struct CacheBlock, assoc);
+ cache->sets[i].lru_gen_counter = 0;
}
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;
}
@@ -149,12 +271,21 @@ static int get_invalid_block(struct Cache *cache,
uint64_t set)
return -1;
}
-static int get_replaced_block(struct Cache *cache)
+static int get_replaced_block(struct 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);
+ defalut:
+ g_assert_not_reached();
+ }
}
-static bool in_cache(struct Cache *cache, uint64_t addr)
+static int in_cache(struct Cache *cache, uint64_t addr)
{
int i;
uint64_t tag, set;
@@ -165,11 +296,11 @@ static bool in_cache(struct 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;
}
/**
@@ -178,24 +309,32 @@ static bool in_cache(struct Cache *cache, uint64_t addr)
* @addr: The address of the requested memory location
*
* Returns true if the requsted data is hit in the cache and false when missed.
- * The cache is updated on miss for the next access.
+ * The cache is then updated for subsequent accesses.
*/
static bool access_cache(struct 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;
@@ -302,6 +441,10 @@ static void free_cache(struct Cache *cache)
g_free(cache->sets[i].blocks);
}
+ if (metadata_destroy) {
+ metadata_destroy(cache);
+ }
+
g_free(cache->sets);
g_free(cache);
}
@@ -389,6 +532,28 @@ static void plugin_exit()
g_mutex_unlock(&mtx);
}
+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)
@@ -408,7 +573,7 @@ int qemu_plugin_install(qemu_plugin_id_t id, const
qemu_info_t *info,
iblksize = 64;
icachesize = iblksize * iassoc * 32;
- rng = g_rand_new();
+ policy = LRU;
for (i = 0; i < argc; i++) {
char *opt = argv[i];
@@ -436,12 +601,26 @@ int qemu_plugin_install(qemu_plugin_id_t id, const
qemu_info_t *info,
g_strfreev(toks);
} 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) {
fprintf(stderr, "dcache cannot be constructed from given
parameters\n");
--
2.25.1
