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 <colyli@suse.de>
Reviewed-by: Michael Lyle <mlyle@lyle.org>
Reviewed-by: Tang Junhui <tang.junhui@zte.com.cn>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 5f7b0b2..9117da5 100644 (file)
--- 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 9e30713..bf3a48a 100644 (file)
--- 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 553e841..d13e4cc 100644 (file)
--- 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 6d26927..f102b1f 100644 (file)
--- 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]))