[PATCH] regmap: rbtree: When adding a reg do a bsearch for target node

[PATCH] regmap: rbtree: When adding a reg do a bsearch for target node

[Nikesh Oswal]

From: Nikesh Oswal <Nikesh.Oswal@wolfsonmicro.com>

A binary search is much more efficient rather than iterating
over the rbtree in ascending order which the current code is
doing.

During initialisation the reg defaults are written to the
cache in a large chunk and these are always sorted in the
ascending order so for this situation ideally we should have
iterated the rbtree in descending order.

But at runtime the drivers may write into the cache in any
random order so this patch selects to use a bsearch to give
an optimal runtime performance and also at initialisation
time when reg defaults are written the performance of binary
search would be much better than iterating in ascending order
which the current code was doing.
  
Signed-off-by: Nikesh Oswal <Nikesh.Oswal@wolfsonmicro.com>
---
 drivers/base/regmap/regcache-rbtree.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/base/regmap/regcache-rbtree.c b/drivers/base/regmap/regcache-rbtree.c
index 56486d9..353f602 100644
--- a/drivers/base/regmap/regcache-rbtree.c
+++ b/drivers/base/regmap/regcache-rbtree.c
@@ -413,8 +413,8 @@ static int regcache_rbtree_write(struct regmap *map, unsigned int reg,
 		max = reg + max_dist;
 
 		/* look for an adjacent register to the one we are about to add */
-		for (node = rb_first(&rbtree_ctx->root); node;
-		     node = rb_next(node)) {
+		node = rbtree_ctx->root.rb_node;
+		while (node) {
 			rbnode_tmp = rb_entry(node, struct regcache_rbtree_node,
 					      node);
 
@@ -425,6 +425,11 @@ static int regcache_rbtree_write(struct regmap *map, unsigned int reg,
 				new_base_reg = min(reg, base_reg);
 				new_top_reg = max(reg, top_reg);
 			} else {
+				if (max < base_reg)
+					node = node->rb_left;
+				else
+					node = node->rb_right;
+
 				continue;
 			}
 
-- 
1.7.9.5

Re: [PATCH] regmap: rbtree: When adding a reg do a bsearch for target node

[Charles Keepax]

On Wed, Oct 21, 2015 at 02:16:14PM +0100, Nikesh Oswal wrote:
> From: Nikesh Oswal <Nikesh.Oswal@wolfsonmicro.com>

If you are going to use your non-opensource email, might as well
use the cirrus one here.

> 
> A binary search is much more efficient rather than iterating
> over the rbtree in ascending order which the current code is
> doing.
> 
> During initialisation the reg defaults are written to the
> cache in a large chunk and these are always sorted in the
> ascending order so for this situation ideally we should have
> iterated the rbtree in descending order.
> 
> But at runtime the drivers may write into the cache in any
> random order so this patch selects to use a bsearch to give
> an optimal runtime performance and also at initialisation
> time when reg defaults are written the performance of binary
> search would be much better than iterating in ascending order
> which the current code was doing.
>   
> Signed-off-by: Nikesh Oswal <Nikesh.Oswal@wolfsonmicro.com>
> ---

Patch looks fine to me though:

Reviewed-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>

Thanks,
Charles