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authorOmar Sandoval <osandov@fb.com>2016-09-17 01:28:25 -0700
committerJens Axboe <axboe@fb.com>2016-09-17 08:39:14 -0600
commit98d95416dbfaf4910caadfb4ddc75e4aacbdff8c (patch)
treeed6a08e6d4358da522265ac1e6a595fe8db35572
parentf4a644db86669d938c71f19560aebf69d4720d63 (diff)
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sbitmap: randomize initial alloc_hint values
In order to get good cache behavior from a sbitmap, we want each CPU to stick to its own cacheline(s) as much as possible. This might happen naturally as the bitmap gets filled up and the alloc_hint values spread out, but we really want this behavior from the start. blk-mq apparently intended to do this, but the code to do this was never wired up. Get rid of the dead code and make it part of the sbitmap library. Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
-rw-r--r--block/blk-mq-tag.c8
-rw-r--r--block/blk-mq-tag.h1
-rw-r--r--lib/sbitmap.c6
3 files changed, 6 insertions, 9 deletions
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index e1c2bedb0bf9..cef618f6fc92 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -7,7 +7,6 @@
*/
#include <linux/kernel.h>
#include <linux/module.h>
-#include <linux/random.h>
#include <linux/blk-mq.h>
#include "blk.h"
@@ -419,13 +418,6 @@ void blk_mq_free_tags(struct blk_mq_tags *tags)
kfree(tags);
}
-void blk_mq_tag_init_last_tag(struct blk_mq_tags *tags, unsigned int *tag)
-{
- unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
-
- *tag = prandom_u32() % depth;
-}
-
int blk_mq_tag_update_depth(struct blk_mq_tags *tags, unsigned int tdepth)
{
tdepth -= tags->nr_reserved_tags;
diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
index f90b850ce43d..09f4cc0aaa84 100644
--- a/block/blk-mq-tag.h
+++ b/block/blk-mq-tag.h
@@ -30,7 +30,6 @@ extern void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
unsigned int tag);
extern bool blk_mq_has_free_tags(struct blk_mq_tags *tags);
extern ssize_t blk_mq_tag_sysfs_show(struct blk_mq_tags *tags, char *page);
-extern void blk_mq_tag_init_last_tag(struct blk_mq_tags *tags, unsigned int *last_tag);
extern int blk_mq_tag_update_depth(struct blk_mq_tags *tags, unsigned int depth);
extern void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool);
void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index be55f744b771..928b82a733f2 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -15,6 +15,7 @@
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
+#include <linux/random.h>
#include <linux/sbitmap.h>
int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
@@ -211,6 +212,11 @@ int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
return -ENOMEM;
}
+ if (depth && !round_robin) {
+ for_each_possible_cpu(i)
+ *per_cpu_ptr(sbq->alloc_hint, i) = prandom_u32() % depth;
+ }
+
sbq->wake_batch = sbq_calc_wake_batch(depth);
atomic_set(&sbq->wake_index, 0);