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OPTIM: pool: improve needed_avg cache line access pattern 

On an AMD EPYC 3rd gen, 20% of the CPU is spent calculating the amount
of pools needed when using QUIC, because pool allocations/releases are
quite frequent and the inter-CCX communication is super slow. Still,
there's a way to save between 0.5 and 1% CPU by using fetch-add and
sub-fetch that are converted to XADD so that the result is directly
fed into the swrate_add argument without having to re-read the memory
area. That's what this patch does.
This commit is contained in:
Willy Tarreau 2024-07-08 18:28:54 +02:00
parent 9797a7718c
commit 87d269707b
1 changed files with 10 additions and 6 deletions
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16
src/pool.c
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@ -424,15 +424,17 @@ void *pool_alloc_nocache(struct pool_head *pool, const void *caller)
{
void *ptr = NULL;
uint bucket;
uint used;
ptr = pool_get_from_os_noinc(pool);
if (!ptr)
return NULL;
bucket = pool_pbucket(ptr);
swrate_add_scaled_opportunistic(&pool->buckets[bucket].needed_avg, POOL_AVG_SAMPLES, pool->buckets[bucket].used, POOL_AVG_SAMPLES/4);
_HA_ATOMIC_INC(&pool->buckets[bucket].allocated);
_HA_ATOMIC_INC(&pool->buckets[bucket].used);
used = _HA_ATOMIC_FETCH_ADD(&pool->buckets[bucket].used, 1);
swrate_add_scaled_opportunistic(&pool->buckets[bucket].needed_avg, POOL_AVG_SAMPLES, used, POOL_AVG_SAMPLES/4);
/* keep track of where the element was allocated from */
POOL_DEBUG_SET_MARK(pool, ptr);
@ -447,10 +449,11 @@ void *pool_alloc_nocache(struct pool_head *pool, const void *caller)
void pool_free_nocache(struct pool_head *pool, void *ptr)
{
uint bucket = pool_pbucket(ptr);
uint used;
_HA_ATOMIC_DEC(&pool->buckets[bucket].used);
used = _HA_ATOMIC_SUB_FETCH(&pool->buckets[bucket].used, 1);
_HA_ATOMIC_DEC(&pool->buckets[bucket].allocated);
swrate_add_opportunistic(&pool->buckets[bucket].needed_avg, POOL_AVG_SAMPLES, pool->buckets[bucket].used);
swrate_add_opportunistic(&pool->buckets[bucket].needed_avg, POOL_AVG_SAMPLES, used);
pool_put_to_os_nodec(pool, ptr);
}
@ -519,6 +522,7 @@ static void pool_evict_last_items(struct pool_head *pool, struct pool_cache_head
uint cluster = 0;
uint to_free_max;
uint bucket;
uint used;
BUG_ON(pool_debugging & POOL_DBG_NO_CACHE);
@ -534,8 +538,8 @@ static void pool_evict_last_items(struct pool_head *pool, struct pool_cache_head
LIST_DELETE(&item->by_lru);
bucket = pool_pbucket(item);
_HA_ATOMIC_DEC(&pool->buckets[bucket].used);
swrate_add_opportunistic(&pool->buckets[bucket].needed_avg, POOL_AVG_SAMPLES, pool->buckets[bucket].used);
used = _HA_ATOMIC_SUB_FETCH(&pool->buckets[bucket].used, 1);
swrate_add_opportunistic(&pool->buckets[bucket].needed_avg, POOL_AVG_SAMPLES, used);
if (to_free_max > released || cluster) {
/* will never match when global pools are disabled */