[PATCH 2/2] blk-stat: add a poll_size value to the request_queue struct

[Sagi Grimberg]

On 26/03/17 05:18, sbates at raithlin.com wrote:
> From: Stephen Bates <sbates at raithlin.com>
>
> In order to bucket IO for the polling algorithm we use a sysfs entry
> to set the filter value. It is signed and we will use that as follows:
>
>  0   : No filtering. All IO are considered in stat generation
>  > 0 : Filtering based on IO of exactly this size only.
>  < 0 : Filtering based on IO less than or equal to -1 time this value.

I'd say that this is a fairly non-trivial semantic meanning to this...

Is there any use for the size exact match filter? If not then
I suggest we always make it (<=) in its semantics...

> Use this member to implement a new bucket function for the io polling
> stats.
>
> Signed-off-by: Stephen Bates <sbates at raithlin.com>
> ---
>  block/blk-mq.c         | 17 +++++++++++++++--
>  block/blk-sysfs.c      | 30 ++++++++++++++++++++++++++++++
>  include/linux/blkdev.h |  1 +
>  3 files changed, 46 insertions(+), 2 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 5ff66f2..5ea9481 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2327,6 +2327,18 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
>  	blk_mq_sysfs_register(q);
>  }
>
> +int blk_mq_poll_stats_bucket(const struct request *rq)
> +{
> +	int val = rq->q->poll_size;
> +
> +	if ((val == 0) ||
> +	    (val > 0 && blk_rq_bytes(rq) == val) ||
> +	    (val < 0 && blk_rq_bytes(rq) <= -val))
> +		return (int)rq_data_dir(rq);
> +
> +	return -1;
> +}
> +
>  struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
>  						  struct request_queue *q)
>  {
> @@ -2338,7 +2350,7 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
>  		goto err_exit;
>
>  	q->poll_cb = blk_stat_alloc_callback(blk_mq_poll_stats_fn,
> -					     blk_stat_rq_ddir, 2, q);
> +					     blk_mq_poll_stats_bucket, 2, q);
>  	if (!q->poll_cb)
>  		goto err_exit;
>
> @@ -2387,9 +2399,10 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
>  	q->nr_requests = set->queue_depth;
>
>  	/*
> -	 * Default to classic polling
> +	 * Default to classic polling. Default to considering all IO.
>  	 */
>  	q->poll_nsec = -1;
> +	q->poll_size = 0;
>
>  	if (set->ops->complete)
>  		blk_queue_softirq_done(q, set->ops->complete);
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index fa831cb..000d5db 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -394,6 +394,29 @@ static ssize_t queue_poll_delay_store(struct request_queue *q, const char *page,
>  	return count;
>  }
>
> +static ssize_t queue_poll_size_show(struct request_queue *q, char *page)
> +{
> +	return sprintf(page, "%d\n", q->poll_size);
> +}
> +
> +static ssize_t queue_poll_size_store(struct request_queue *q, const char *page,
> +				     size_t count)
> +{
> +	int err, val;
> +
> +	if (!q->mq_ops || !q->mq_ops->poll)
> +		return -EINVAL;
> +
> +	err = kstrtoint(page, 10, &val);
> +	if (err < 0)
> +		return err;
> +
> +	q->poll_size = val;
> +
> +	return count;
> +}
> +
> +
>  static ssize_t queue_poll_show(struct request_queue *q, char *page)
>  {
>  	return queue_var_show(test_bit(QUEUE_FLAG_POLL, &q->queue_flags), page);
> @@ -654,6 +677,12 @@ static struct queue_sysfs_entry queue_poll_entry = {
>  	.store = queue_poll_store,
>  };
>
> +static struct queue_sysfs_entry queue_poll_size_entry = {
> +	.attr = {.name = "io_poll_size", .mode = S_IRUGO | S_IWUSR },
> +	.show = queue_poll_size_show,
> +	.store = queue_poll_size_store,
> +};
> +
>  static struct queue_sysfs_entry queue_poll_delay_entry = {
>  	.attr = {.name = "io_poll_delay", .mode = S_IRUGO | S_IWUSR },
>  	.show = queue_poll_delay_show,
> @@ -710,6 +739,7 @@ static struct attribute *default_attrs[] = {
>  	&queue_dax_entry.attr,
>  	&queue_wb_lat_entry.attr,
>  	&queue_poll_delay_entry.attr,
> +	&queue_poll_size_entry.attr,
>  	NULL,
>  };
>
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 1a7dc42..7ff5388 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -517,6 +517,7 @@ struct request_queue {
>
>  	unsigned int		rq_timeout;
>  	int			poll_nsec;
> +	int			poll_size;
>
>  	struct blk_stat_callback	*poll_cb;
>  	struct blk_rq_stat	poll_stat[2];
>