Commit 3d3472f3 authored Feb 16, 2022 by Chaitanya Kulkarni Committed by Jens Axboe Feb 27, 2022

null_blk: remove hardcoded alloc_cmd() parameter



Only caller of alloc_cmd() is null_submit_bio() unconditionally sets
second parameter to true and that is statically hard-coded in null_blk.
There is no point in having statically hardcoded function parameter.

Remove the unnecessary parameter can_wait and adjust the code so it
can retain existing behavior of waiting when we don't get valid
nullb_cmd from __alloc_cmd() in alloc_cmd().

The restructured code avoids multiple return statements, multiple
calls to __alloc_cmd() and resulting a fast path call to
prepare_to_wait() due to removal of first alloc_cmd() call.

Follow the pattern that we have in bio_alloc() to set the structure
members in the structure allocation function in alloc_cmd() and pass
bio to initialize newly allocated cmd->bio member.

Follow the pattern in copy_to_nullb() to use result of one function call
(null_cache_active()) to be used as a parameter to another function call
(null_insert_page()), use result of alloc_cmd() as a first parameter to
the null_handle_cmd() in null_submit_bio() function. This allow us to
remove the local variable cmd on stack in null_submit_bio() that is in
fast path.

Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Link: https://lore.kernel.org/r/20220216172945.31124-2-kch@nvidia.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent ef44c508

drivers/block/null_blk/main.c

+12 −17

Original line number	Diff line number	Diff line
		@@ -720,26 +720,25 @@ static struct nullb_cmd __alloc_cmd(struct nullb_queue nq)
		return NULL;
		}

		static struct nullb_cmd alloc_cmd(struct nullb_queue nq, int can_wait)
		static struct nullb_cmd alloc_cmd(struct nullb_queue nq, struct bio *bio)
		{
		struct nullb_cmd *cmd;
		DEFINE_WAIT(wait);

		do {
		/*
		* This avoids multiple return statements, multiple calls to
		* __alloc_cmd() and a fast path call to prepare_to_wait().
		*/
		cmd = __alloc_cmd(nq);
		if (cmd \|\| !can_wait)
		if (cmd) {
		cmd->bio = bio;
		return cmd;

		do {
		}
		prepare_to_wait(&nq->wait, &wait, TASK_UNINTERRUPTIBLE);
		cmd = __alloc_cmd(nq);
		if (cmd)
		break;

		io_schedule();
		} while (1);

		finish_wait(&nq->wait, &wait);
		return cmd;
		} while (1);
		}

		static void end_cmd(struct nullb_cmd *cmd)
		@@ -1477,12 +1476,8 @@ static void null_submit_bio(struct bio *bio)
		sector_t nr_sectors = bio_sectors(bio);
		struct nullb *nullb = bio->bi_bdev->bd_disk->private_data;
		struct nullb_queue *nq = nullb_to_queue(nullb);
		struct nullb_cmd *cmd;

		cmd = alloc_cmd(nq, 1);
		cmd->bio = bio;

		null_handle_cmd(cmd, sector, nr_sectors, bio_op(bio));
		null_handle_cmd(alloc_cmd(nq, bio), sector, nr_sectors, bio_op(bio));
		}

		static bool should_timeout_request(struct request *rq)