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qcow2: remove qcow2_cache_find_entry_to_replace() 

A cache miss means that the whole array was traversed and the entry
we were looking for was not found, so there's no need to traverse it
again in order to select an entry to replace.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Alberto Garcia 2015-05-11 15:54:56 +03:00 committed by Kevin Wolf
parent 2693310ecc
commit fdfbca82a0
1 changed files with 16 additions and 29 deletions
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45
block/qcow2-cache.c
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@ -242,51 +242,38 @@ int qcow2_cache_empty(BlockDriverState *bs, Qcow2Cache *c)
return 0;
}
static int qcow2_cache_find_entry_to_replace(Qcow2Cache *c)
{
int i;
uint64_t min_lru_counter = UINT64_MAX;
int min_index = -1;
for (i = 0; i < c->size; i++) {
if (c->entries[i].ref) {
continue;
}
if (c->entries[i].lru_counter < min_lru_counter) {
min_index = i;
min_lru_counter = c->entries[i].lru_counter;
}
}
if (min_index == -1) {
/* This can't happen in current synchronous code, but leave the check
* here as a reminder for whoever starts using AIO with the cache */
abort();
}
return min_index;
}
static int qcow2_cache_do_get(BlockDriverState *bs, Qcow2Cache *c,
uint64_t offset, void **table, bool read_from_disk)
{
BDRVQcowState *s = bs->opaque;
int i;
int ret;
uint64_t min_lru_counter = UINT64_MAX;
int min_lru_index = -1;
trace_qcow2_cache_get(qemu_coroutine_self(), c == s->l2_table_cache,
offset, read_from_disk);
/* Check if the table is already cached */
for (i = 0; i < c->size; i++) {
if (c->entries[i].offset == offset) {
const Qcow2CachedTable *t = &c->entries[i];
if (t->offset == offset) {
goto found;
}
if (t->ref == 0 && t->lru_counter < min_lru_counter) {
min_lru_counter = t->lru_counter;
min_lru_index = i;
}
}
/* If not, write a table back and replace it */
i = qcow2_cache_find_entry_to_replace(c);
if (min_lru_index == -1) {
/* This can't happen in current synchronous code, but leave the check
* here as a reminder for whoever starts using AIO with the cache */
abort();
}
/* Cache miss: write a table back and replace it */
i = min_lru_index;
trace_qcow2_cache_get_replace_entry(qemu_coroutine_self(),
c == s->l2_table_cache, i);
if (i < 0) {