From 2831231d4c3f999d2d062b23dfbc8b0faa4bc6e0 Mon Sep 17 00:00:00 2001
From: Coly Li <colyli@suse.de>
Date: Mon, 8 Jan 2018 12:21:28 -0800
Subject: [PATCH] bcache: reduce cache_set devices iteration by
devices_max_used
Git-commit: 2831231d4c3f999d2d062b23dfbc8b0faa4bc6e0
Patch-mainline: v4.16-rc1
References: bsc#1093023
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>
---
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]))
--
2.16.3