From: Omar Sandoval <osandov@xxxxxx>
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 last_cache 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@xxxxxx>
---
block/blk-mq-tag.c | 8 --------
block/blk-mq-tag.h | 1 -
lib/sbitmap.c | 6 ++++++
3 files changed, 6 insertions(+), 9 deletions(-)
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index e1c2bed..cef618f 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 f90b850..09f4cc0 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 3a91269..d873bb0a 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,
@@ -208,6 +209,11 @@ 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_WAKE_BATCH;
if (sbq->wake_batch > depth / SBQ_WAIT_QUEUES)
sbq->wake_batch = max(1U, depth / SBQ_WAIT_QUEUES);
--
2.9.3
--
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