[PATCH v4 31/38] drm: Optimise power-of-two alignments in drm_mm_scan_add_block()

Chris Wilson
2016-12-22T08:36:34Z

For power-of-two alignments, we can avoid the 64bit divide and do a
simple bitwise add instead.

v2: s/alignment_mask/remainder_mask/

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
---
drivers/gpu/drm/drm_mm.c | 9 ++++++++-
include/drm/drm_mm.h | 1 +
2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
index 189ab84c5a59..0441d84fba74 100644
--- a/drivers/gpu/drm/drm_mm.c
+++ b/drivers/gpu/drm/drm_mm.c
@@ -742,8 +742,12 @@ void drm_mm_scan_init_with_range(struct drm_mm_scan *scan,

scan->mm = mm;

+ if (alignment <= 1)
+ alignment = 0;
+
scan->color = color;
scan->alignment = alignment;
+ scan->remainder_mask = is_power_of_2(alignment) ? alignment - 1 : 0;
scan->size = size;
scan->flags = flags;

@@ -811,7 +815,10 @@ bool drm_mm_scan_add_block(struct drm_mm_scan *scan,
if (scan->alignment) {
u64 rem;

- div64_u64_rem(adj_start, scan->alignment, &rem);
+ if (likely(scan->remainder_mask))
+ rem = adj_start & scan->remainder_mask;
+ else
+ div64_u64_rem(adj_start, scan->alignment, &rem);
if (rem) {
adj_start -= rem;
if (scan->flags != DRM_MM_CREATE_TOP)
diff --git a/include/drm/drm_mm.h b/include/drm/drm_mm.h
index 606336fc229a..d6701d56ea74 100644
--- a/include/drm/drm_mm.h
+++ b/include/drm/drm_mm.h
@@ -110,6 +110,7 @@ struct drm_mm_scan {

u64 size;
u64 alignment;
+ u64 remainder_mask;

u64 range_start;
u64 range_end;
--
2.11.0

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