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blk-mq: optimise rq sort function

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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.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2019-11-29 00:11:53 +03:00 committed by Jens Axboe
parent 80a0c2e511
commit 7d30a62102
1 changed files with 4 additions and 8 deletions
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12
block/blk-mq.c
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@ -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);
}