On 09/03/2014 02:33 PM, Alexander Gordeev wrote:
> Signed-off-by: Alexander Gordeev <agord...@redhat.com>
> Cc: Jens Axboe <ax...@kernel.dk>
> ---
> block/blk-mq-tag.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> index 4953b64..d1eb579 100644
> --- a/block/blk-mq-tag.c
> +++ b/block/blk-mq-tag.c
> @@ -60,8 +60,7 @@ static inline void bt_index_atomic_inc(atomic_t *index)
> */
> void __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
> {
> - if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) &&
> - !test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
> + if (!test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
> atomic_inc(&hctx->tags->active_queues);
That's done on purpose as well, it's a lot faster to do the (non-atomic)
check first and only do the expensive test and set if needed.
See 7fcbbaf18392 for similar construct and actual numbers on a real case.
--
Jens Axboe
--
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