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authorJens Axboe <axboe@fb.com>2016-08-25 08:07:30 -0600
committerJens Axboe <axboe@fb.com>2016-08-29 08:13:21 -0600
commit88c7b2b75132c3ff8180b71e4f06cf043a00eac8 (patch)
treefa40cb8073832b2321b3f28a3fd782c125364dfb /block/blk-mq.c
parent8d354f133e86dd03ea7885a91df398c55ff699ff (diff)
downloadblackbird-op-linux-88c7b2b75132c3ff8180b71e4f06cf043a00eac8.tar.gz
blackbird-op-linux-88c7b2b75132c3ff8180b71e4f06cf043a00eac8.zip
blk-mq: prefetch request in blk_mq_tag_to_rq()
When drivers or the core calls this function, they usually dereference the request shortly there after. Prefetch the first cache line. Profiling IO workloads shows that this is the most common cache miss on the block side of things. Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'block/blk-mq.c')
-rw-r--r--block/blk-mq.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c
index b68fdcbe58f6..eea0d230faa1 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -22,6 +22,7 @@
#include <linux/sched/sysctl.h>
#include <linux/delay.h>
#include <linux/crash_dump.h>
+#include <linux/prefetch.h>
#include <trace/events/block.h>
@@ -588,8 +589,10 @@ EXPORT_SYMBOL(blk_mq_abort_requeue_list);
struct request *blk_mq_tag_to_rq(struct blk_mq_tags *tags, unsigned int tag)
{
- if (tag < tags->nr_tags)
+ if (tag < tags->nr_tags) {
+ prefetch(tags->rqs[tag]);
return tags->rqs[tag];
+ }
return NULL;
}
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