From: Ming Lei <ming.lei@redhat.com>
To: Bart Van Assche <bvanassche@acm.org>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
Jaegeuk Kim <jaegeuk@kernel.org>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
Martijn Coenen <maco@android.com>
Subject: Re: [PATCH 1/2] loop: Prevent that an I/O scheduler is assigned
Date: Tue, 3 Aug 2021 09:54:18 +0800 [thread overview]
Message-ID: <YQihyvnN3msaNyDW@T590> (raw)
In-Reply-To: <20210803000200.4125318-2-bvanassche@acm.org>
On Mon, Aug 02, 2021 at 05:01:59PM -0700, Bart Van Assche wrote:
> Loop devices have a single hardware queue. Hence, the block layer function
> elevator_get_default() selects the mq-deadline scheduler for loop devices.
> Using the mq-deadline scheduler or any other I/O scheduler for loop devices
> incurs unnecessary overhead. Make the loop driver pass the flag
> BLK_MQ_F_NOSCHED to the block layer core such that no I/O scheduler can be
> associated with block devices. This approach has an advantage compared to
> letting udevd change the loop I/O scheduler to none, namely that
> synchronize_rcu() does not get called.
>
> It is intentional that the flag BLK_MQ_F_SHOULD_MERGE is preserved.
>
> This patch reduces the Android boot time on my test setup with 0.5 seconds.
Can you investigate why none reduces Android boot time? Or reproduce &
understand it by a fio simulation on your setting?
>
> Cc: Ming Lei <ming.lei@redhat.com>
> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Martijn Coenen <maco@android.com>
> Cc: Jaegeuk Kim <jaegeuk@kernel.org>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
> drivers/block/loop.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index f8486d9b75a4..9fca3ab3988d 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -2333,7 +2333,8 @@ static int loop_add(int i)
> lo->tag_set.queue_depth = 128;
> lo->tag_set.numa_node = NUMA_NO_NODE;
> lo->tag_set.cmd_size = sizeof(struct loop_cmd);
> - lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_STACKING;
> + lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_STACKING |
> + BLK_MQ_F_NO_SCHED;
Loop directio needs io merge, so it isn't good to set NO_SCHED
unconditionally, see:
40326d8a33d5 ("block/loop: allow request merge for directio mode")
Thanks,
Ming
next prev parent reply other threads:[~2021-08-03 1:54 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-03 0:01 [PATCH 0/2] Two loop driver patches Bart Van Assche
2021-08-03 0:01 ` [PATCH 1/2] loop: Prevent that an I/O scheduler is assigned Bart Van Assche
2021-08-03 1:54 ` Ming Lei [this message]
2021-08-03 5:23 ` Bart Van Assche
2021-08-03 7:18 ` Ming Lei
2021-08-03 0:02 ` [PATCH 2/2] loop: Add the default_queue_depth kernel module parameter Bart Van Assche
2021-08-03 1:57 ` Ming Lei
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