Re: [PATCH 10/17] block/cfq: replace cfq_rb_root leftmost caching

[Jan Kara]

On Tue 18-07-17 18:45:56, Davidlohr Bueso wrote:
> ... with the generic rbtree flavor instead. No changes
> in semantics whatsoever.
> 
> Cc: axboe@xxxxxx
> Cc: linux-block@xxxxxxxxxxxxxxx
> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  block/cfq-iosched.c | 70 +++++++++++++++--------------------------------------
>  1 file changed, 20 insertions(+), 50 deletions(-)
> 
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 3d5c28945719..92c31683a2bb 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -93,13 +93,12 @@ struct cfq_ttime {
>   * move this into the elevator for the rq sorting as well.
>   */
>  struct cfq_rb_root {
> -	struct rb_root rb;
> -	struct rb_node *left;
> +	struct rb_root_cached rb;
>  	unsigned count;
>  	u64 min_vdisktime;
>  	struct cfq_ttime ttime;
>  };
> -#define CFQ_RB_ROOT	(struct cfq_rb_root) { .rb = RB_ROOT, \
> +#define CFQ_RB_ROOT	(struct cfq_rb_root) { .rb = RB_ROOT_CACHED, \
>  			.ttime = {.last_end_request = ktime_get_ns(),},}
>  
>  /*
> @@ -984,10 +983,9 @@ static inline u64 max_vdisktime(u64 min_vdisktime, u64 vdisktime)
>  
>  static void update_min_vdisktime(struct cfq_rb_root *st)
>  {
> -	struct cfq_group *cfqg;
> +	if (!RB_EMPTY_ROOT(&st->rb.rb_root)) {
> +		struct cfq_group *cfqg = rb_entry_cfqg(st->rb.rb_leftmost);
>  
> -	if (st->left) {
> -		cfqg = rb_entry_cfqg(st->left);
>  		st->min_vdisktime = max_vdisktime(st->min_vdisktime,
>  						  cfqg->vdisktime);
>  	}
> @@ -1169,46 +1167,25 @@ cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2,
>  	}
>  }
>  
> -/*
> - * The below is leftmost cache rbtree addon
> - */
>  static struct cfq_queue *cfq_rb_first(struct cfq_rb_root *root)
>  {
>  	/* Service tree is empty */
>  	if (!root->count)
>  		return NULL;
>  
> -	if (!root->left)
> -		root->left = rb_first(&root->rb);
> -
> -	if (root->left)
> -		return rb_entry(root->left, struct cfq_queue, rb_node);
> -
> -	return NULL;
> +	return rb_entry(rb_first_cached(&root->rb), struct cfq_queue, rb_node);
>  }
>  
>  static struct cfq_group *cfq_rb_first_group(struct cfq_rb_root *root)
>  {
> -	if (!root->left)
> -		root->left = rb_first(&root->rb);
> -
> -	if (root->left)
> -		return rb_entry_cfqg(root->left);
> -
> -	return NULL;
> +	return rb_entry_cfqg(rb_first_cached(&root->rb));
>  }
>  
> -static void rb_erase_init(struct rb_node *n, struct rb_root *root)
> +static void cfq_rb_erase(struct rb_node *n, struct cfq_rb_root *root)
>  {
> -	rb_erase(n, root);
> +	rb_erase_cached(n, &root->rb);
>  	RB_CLEAR_NODE(n);
> -}
>  
> -static void cfq_rb_erase(struct rb_node *n, struct cfq_rb_root *root)
> -{
> -	if (root->left == n)
> -		root->left = NULL;
> -	rb_erase_init(n, &root->rb);
>  	--root->count;
>  }
>  
> @@ -1258,11 +1235,11 @@ cfqg_key(struct cfq_rb_root *st, struct cfq_group *cfqg)
>  static void
>  __cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
>  {
> -	struct rb_node **node = &st->rb.rb_node;
> +	struct rb_node **node = &st->rb.rb_root.rb_node;
>  	struct rb_node *parent = NULL;
>  	struct cfq_group *__cfqg;
>  	s64 key = cfqg_key(st, cfqg);
> -	int left = 1;
> +	bool leftmost = true;
>  
>  	while (*node != NULL) {
>  		parent = *node;
> @@ -1272,15 +1249,12 @@ __cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
>  			node = &parent->rb_left;
>  		else {
>  			node = &parent->rb_right;
> -			left = 0;
> +			leftmost = false;
>  		}
>  	}
>  
> -	if (left)
> -		st->left = &cfqg->rb_node;
> -
>  	rb_link_node(&cfqg->rb_node, parent, node);
> -	rb_insert_color(&cfqg->rb_node, &st->rb);
> +	rb_insert_color_cached(&cfqg->rb_node, &st->rb, leftmost);
>  }
>  
>  /*
> @@ -1381,7 +1355,7 @@ cfq_group_notify_queue_add(struct cfq_data *cfqd, struct cfq_group *cfqg)
>  	 * so that groups get lesser vtime based on their weights, so that
>  	 * if group does not loose all if it was not continuously backlogged.
>  	 */
> -	n = rb_last(&st->rb);
> +	n = rb_last(&st->rb.rb_root);
>  	if (n) {
>  		__cfqg = rb_entry_cfqg(n);
>  		cfqg->vdisktime = __cfqg->vdisktime +
> @@ -2223,14 +2197,14 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
>  	struct cfq_queue *__cfqq;
>  	u64 rb_key;
>  	struct cfq_rb_root *st;
> -	int left;
> +	bool leftmost = true;
>  	int new_cfqq = 1;
>  	u64 now = ktime_get_ns();
>  
>  	st = st_for(cfqq->cfqg, cfqq_class(cfqq), cfqq_type(cfqq));
>  	if (cfq_class_idle(cfqq)) {
>  		rb_key = CFQ_IDLE_DELAY;
> -		parent = rb_last(&st->rb);
> +		parent = rb_last(&st->rb.rb_root);
>  		if (parent && parent != &cfqq->rb_node) {
>  			__cfqq = rb_entry(parent, struct cfq_queue, rb_node);
>  			rb_key += __cfqq->rb_key;
> @@ -2264,10 +2238,9 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
>  		cfqq->service_tree = NULL;
>  	}
>  
> -	left = 1;
>  	parent = NULL;
>  	cfqq->service_tree = st;
> -	p = &st->rb.rb_node;
> +	p = &st->rb.rb_root.rb_node;
>  	while (*p) {
>  		parent = *p;
>  		__cfqq = rb_entry(parent, struct cfq_queue, rb_node);
> @@ -2279,16 +2252,13 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
>  			p = &parent->rb_left;
>  		else {
>  			p = &parent->rb_right;
> -			left = 0;
> +			leftmost = false;
>  		}
>  	}
>  
> -	if (left)
> -		st->left = &cfqq->rb_node;
> -
>  	cfqq->rb_key = rb_key;
>  	rb_link_node(&cfqq->rb_node, parent, p);
> -	rb_insert_color(&cfqq->rb_node, &st->rb);
> +	rb_insert_color_cached(&cfqq->rb_node, &st->rb, leftmost);
>  	st->count++;
>  	if (add_front || !new_cfqq)
>  		return;
> @@ -2735,7 +2705,7 @@ static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
>  	/* There is nothing to dispatch */
>  	if (!st)
>  		return NULL;
> -	if (RB_EMPTY_ROOT(&st->rb))
> +	if (RB_EMPTY_ROOT(&st->rb.rb_root))
>  		return NULL;
>  	return cfq_rb_first(st);
>  }
> @@ -3221,7 +3191,7 @@ static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd)
>  	struct cfq_rb_root *st = &cfqd->grp_service_tree;
>  	struct cfq_group *cfqg;
>  
> -	if (RB_EMPTY_ROOT(&st->rb))
> +	if (RB_EMPTY_ROOT(&st->rb.rb_root))
>  		return NULL;
>  	cfqg = cfq_rb_first_group(st);
>  	update_min_vdisktime(st);
> -- 
> 2.12.0
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR