Re: [PATCH 6/9] block/mq-deadline: Reduce the read expiry time for non-rotational media

[Himanshu Madhani <himanshu.madhani@oracle.com>]

On 5/26/21 8:01 PM, Bart Van Assche wrote:
> Rotational media (hard disks) benefit more from merging requests than
> non-rotational media. Reduce the read expire time for non-rotational media
> to reduce read latency.
> 
> Cc: Damien Le Moal <damien.lemoal@wdc.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Ming Lei <ming.lei@redhat.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>   block/mq-deadline.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/block/mq-deadline.c b/block/mq-deadline.c
> index dfbc6b77fa71..2ab844a4b6b5 100644
> --- a/block/mq-deadline.c
> +++ b/block/mq-deadline.c
> @@ -29,7 +29,9 @@
>   /*
>    * See Documentation/block/deadline-iosched.rst
>    */
> -static const int read_expire = HZ / 2;  /* max time before a read is submitted. */
> +/* max time before a read is submitted. */
> +static const int read_expire_rot = HZ / 2;
> +static const int read_expire_nonrot = 1;
>   static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
>   static const int writes_starved = 2;    /* max times reads can starve a write */
>   static const int fifo_batch = 16;       /* # of sequential requests treated as one
> @@ -430,7 +432,8 @@ static int dd_init_sched(struct request_queue *q, struct elevator_type *e)
>   	INIT_LIST_HEAD(&dd->fifo_list[DD_WRITE]);
>   	dd->sort_list[DD_READ] = RB_ROOT;
>   	dd->sort_list[DD_WRITE] = RB_ROOT;
> -	dd->fifo_expire[DD_READ] = read_expire;
> +	dd->fifo_expire[DD_READ] = blk_queue_nonrot(q) ? read_expire_nonrot :
> +		read_expire_rot;
>   	dd->fifo_expire[DD_WRITE] = write_expire;
>   	dd->writes_starved = writes_starved;
>   	dd->front_merges = 1;
> 

Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>

-- 
Himanshu Madhani                                Oracle Linux Engineering