[Pixman] [PATCH 1/3] ARM: use prefetch in nearest scaled 'src_0565_0565'

[Siarhei Siamashka]

From: Siarhei Siamashka <siarhei.siamashka at nokia.com>

Benchmark on ARM Cortex-A8 r1p3 @500MHz, 32-bit LPDDR @166MHz:
 Microbenchmark (scaling 2000x2000 image with scale factor close to 1x):
  before: op=1, src=10020565, dst=10020565, speed=75.02 MPix/s
  after:  op=1, src=10020565, dst=10020565, speed=73.63 MPix/s

Benchmark on ARM Cortex-A8 r2p2 @1GHz, 32-bit LPDDR @200MHz:
 Microbenchmark (scaling 2000x2000 image with scale factor close to 1x):
  before: op=1, src=10020565, dst=10020565, speed=176.12 MPix/s
  after:  op=1, src=10020565, dst=10020565, speed=267.50 MPix/s
---
 pixman/pixman-arm-simd-asm.S |   27 +++++++++++++++++++++++++--
 1 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/pixman/pixman-arm-simd-asm.S b/pixman/pixman-arm-simd-asm.S
index 7567700..dd1366d 100644
--- a/pixman/pixman-arm-simd-asm.S
+++ b/pixman/pixman-arm-simd-asm.S
@@ -348,6 +348,7 @@ pixman_asm_function pixman_scaled_nearest_scanline_0565_0565_SRC_asm_armv6
 	TMP1	.req	r4
 	TMP2	.req	r5
 	VXMASK	.req	r6
+	PF_OFFS	.req	r7
 
 	ldr	UNIT_X, [sp]
 	push	{r4, r5, r6, r7}
@@ -366,12 +367,33 @@ pixman_asm_function pixman_scaled_nearest_scanline_0565_0565_SRC_asm_armv6
 		strh	TMP2, [DST], #2
 	.endm
 
+	/*
+	 * stop prefetch before reaching the end of scanline (a good behaving
+	 * value selected based on some benchmarks with short scanlines)
+	 */
+	#define PREFETCH_BRAKING_DISTANCE 32
+
 	/* now do the scaling */
 	and	TMP1, VXMASK, VX, lsr #15
 	add	VX, VX, UNIT_X
-	subs	W, #4
+	subs	W, #(8 + PREFETCH_BRAKING_DISTANCE)
+	blt	2f
+	/* set prefetch distance to 80 pixels ahead */
+	add	PF_OFFS, VX, UNIT_X, lsl #6
+	add	PF_OFFS, PF_OFFS, UNIT_X, lsl #4
+1:	/* main loop, process 8 pixels per iteration with prefetch */
+	subs	W, W, #8
+	add	PF_OFFS, UNIT_X, lsl #3
+	scale_2_pixels
+	scale_2_pixels
+	scale_2_pixels
+	scale_2_pixels
+	pld	[SRC, PF_OFFS, lsr #15]
+	bge	1b
+2:
+	subs	W, #(4 - 8 - PREFETCH_BRAKING_DISTANCE)
 	blt	2f
-1: /* main loop, process 4 pixels per iteration */
+1:	/* process the remaining pixels */
 	scale_2_pixels
 	scale_2_pixels
 	subs	W, W, #4
@@ -394,6 +416,7 @@ pixman_asm_function pixman_scaled_nearest_scanline_0565_0565_SRC_asm_armv6
 	.unreq	TMP1
 	.unreq	TMP2
 	.unreq	VXMASK
+	.unreq	PF_OFFS
 	/* return */
 	pop	{r4, r5, r6, r7}
 	bx	lr
-- 
1.7.3.4