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authorOmar Sandoval <osandov@fb.com>2016-09-17 11:28:25 +0300
committerJens Axboe <axboe@fb.com>2016-09-17 17:39:14 +0300
commit98d95416dbfaf4910caadfb4ddc75e4aacbdff8c (patch)
treeed6a08e6d4358da522265ac1e6a595fe8db35572 /lib
parentf4a644db86669d938c71f19560aebf69d4720d63 (diff)
downloadlinux-98d95416dbfaf4910caadfb4ddc75e4aacbdff8c.tar.xz
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>
Diffstat (limited to 'lib')
-rw-r--r--lib/sbitmap.c6
1 files changed, 6 insertions, 0 deletions
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);