From 2831231d4c3f999d2d062b23dfbc8b0faa4bc6e0 Mon Sep 17 00:00:00 2001 From: Coly Li Date: Mon, 8 Jan 2018 12:21:28 -0800 Subject: bcache: reduce cache_set devices iteration by devices_max_used 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 Reviewed-by: Michael Lyle Reviewed-by: Tang Junhui Signed-off-by: Jens Axboe --- drivers/md/bcache/writeback.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/md/bcache/writeback.h') 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])) -- cgit