From: Coly Li <colyli@xxxxxxx> Member devices of struct cache_set is used to reference all attached bcache devices to this cache set. If it is treated as array of pointers, size of devices[] is indicated by member nr_uuids of struct cache_set. nr_uuids is calculated in drivers/md/super.c:bch_cache_set_alloc(), bucket_bytes(c) / sizeof(struct uuid_entry) Bucket size is determined by user space tool "make-bcache", by default it is 1024 sectors (defined in bcache-tools/make-bcache.c:main()). So default nr_uuids value is 4096 from the above calculation. Every time when bcache code iterates bcache devices of a cache set, all the 4096 pointers are checked even only 1 bcache device is attached to the cache set, that's a wast of time and unncessary. This patch adds a member devices_max_used to struct cache_set. Its value is 1 + the maximum used index of devices[] in a cache set. When iterating all valid bcache devices of a cache set, use c->devices_max_used in for-loop may reduce a lot of useless checking. Personally, my motivation of this patch is not for performance, I use it in bcache debugging, which helps me to narrow down the scape to check valid bcached devices of a cache set. Signed-off-by: Coly Li <colyli@xxxxxxx> Reviewed-by: Michael Lyle <mlyle@xxxxxxxx> Reviewed-by: Tang Junhui <tang.junhui@xxxxxxxxxx> --- drivers/md/bcache/bcache.h | 1 + drivers/md/bcache/btree.c | 2 +- drivers/md/bcache/super.c | 9 ++++++--- drivers/md/bcache/writeback.h | 2 +- 4 files changed, 9 insertions(+), 5 deletions(-) diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h index 5f7b0b2513cc..9117da5f494b 100644 --- a/drivers/md/bcache/bcache.h +++ b/drivers/md/bcache/bcache.h @@ -497,6 +497,7 @@ struct cache_set { int caches_loaded; struct bcache_device **devices; + unsigned devices_max_used; struct list_head cached_devs; uint64_t cached_dev_sectors; struct closure caching; diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c index 9e30713dbdb8..bf3a48aa9a9a 100644 --- a/drivers/md/bcache/btree.c +++ b/drivers/md/bcache/btree.c @@ -1679,7 +1679,7 @@ static void bch_btree_gc_finish(struct cache_set *c) /* don't reclaim buckets to which writeback keys point */ rcu_read_lock(); - for (i = 0; i < c->nr_uuids; i++) { + for (i = 0; i < c->devices_max_used; i++) { struct bcache_device *d = c->devices[i]; struct cached_dev *dc; struct keybuf_key *w, *n; diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c index 553e841e897d..d13e4ccb30a0 100644 --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -721,6 +721,9 @@ static void bcache_device_attach(struct bcache_device *d, struct cache_set *c, d->c = c; c->devices[id] = d; + if (id >= c->devices_max_used) + c->devices_max_used = id + 1; + closure_get(&c->caching); } @@ -1267,7 +1270,7 @@ static int flash_devs_run(struct cache_set *c) struct uuid_entry *u; for (u = c->uuids; - u < c->uuids + c->nr_uuids && !ret; + u < c->uuids + c->devices_max_used && !ret; u++) if (UUID_FLASH_ONLY(u)) ret = flash_dev_run(c, u); @@ -1433,7 +1436,7 @@ static void __cache_set_unregister(struct closure *cl) mutex_lock(&bch_register_lock); - for (i = 0; i < c->nr_uuids; i++) + for (i = 0; i < c->devices_max_used; i++) if (c->devices[i]) { if (!UUID_FLASH_ONLY(&c->uuids[i]) && test_bit(CACHE_SET_UNREGISTERING, &c->flags)) { @@ -1496,7 +1499,7 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb *sb) c->bucket_bits = ilog2(sb->bucket_size); c->block_bits = ilog2(sb->block_size); c->nr_uuids = bucket_bytes(c) / sizeof(struct uuid_entry); - + c->devices_max_used = 0; c->btree_pages = bucket_pages(c); if (c->btree_pages > BTREE_MAX_PAGES) c->btree_pages = max_t(int, c->btree_pages / 4, diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h index 6d26927267f8..f102b1f9bc51 100644 --- a/drivers/md/bcache/writeback.h +++ b/drivers/md/bcache/writeback.h @@ -24,7 +24,7 @@ static inline uint64_t bcache_flash_devs_sectors_dirty(struct cache_set *c) mutex_lock(&bch_register_lock); - for (i = 0; i < c->nr_uuids; i++) { + for (i = 0; i < c->devices_max_used; i++) { struct bcache_device *d = c->devices[i]; if (!d || !UUID_FLASH_ONLY(&c->uuids[i])) -- 2.14.1