Re: [PATCH 1/3] blk-mq: optimise rq sort function
From: Nikolay Borisov <hidden>
Date: 2019-11-29 08:28:37
Also in:
lkml
On 28.11.19 г. 23:11 ч., Pavel Begunkov wrote:
Check "!=" in multi-layer comparisons. The same memory usage, fewer instructions, and 2 from 4 jumps are replaced with SETcc. Note, that list_sort() doesn't differ 0 and <0. Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
My first reaction was this is wrong since you no longer return negative
values. But then I looked into list_sort/merge and this branch
'if (cmp(priv, a, b) <= 0) {' clearly shows this is correct.
So :
Reviewed-by: Nikolay Borisov <redacted>
quoted hunk ↗ jump to hunk
--- block/blk-mq.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-)diff --git a/block/blk-mq.c b/block/blk-mq.c index 323c9cb28066..f32a3cfdd34e 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c@@ -1668,14 +1668,10 @@ static int plug_rq_cmp(void *priv, struct list_head *a, struct list_head *b) struct request *rqa = container_of(a, struct request, queuelist); struct request *rqb = container_of(b, struct request, queuelist); - if (rqa->mq_ctx < rqb->mq_ctx) - return -1; - else if (rqa->mq_ctx > rqb->mq_ctx) - return 1; - else if (rqa->mq_hctx < rqb->mq_hctx) - return -1; - else if (rqa->mq_hctx > rqb->mq_hctx) - return 1; + if (rqa->mq_ctx != rqb->mq_ctx) + return rqa->mq_ctx > rqb->mq_ctx; + if (rqa->mq_hctx != rqb->mq_hctx) + return rqa->mq_hctx > rqb->mq_hctx; return blk_rq_pos(rqa) > blk_rq_pos(rqb); }