summaryrefslogtreecommitdiffstats
path: root/arch/arm
diff options
context:
space:
mode:
authorFabio Estevam <festevam@gmail.com>2013-11-30 15:24:42 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2013-11-30 22:21:03 +0000
commit11d4bb1bd067f9d01d18f620ccfad516dc579593 (patch)
treeabd79988692f334730e2c245a5bd8db56b46e03b /arch/arm
parente2ccba49085ab5d71b092de2a5176eb9b19cc876 (diff)
downloadop-kernel-dev-11d4bb1bd067f9d01d18f620ccfad516dc579593.zip
op-kernel-dev-11d4bb1bd067f9d01d18f620ccfad516dc579593.tar.gz
ARM: 7907/1: lib: delay-loop: Add align directive to fix BogoMIPS calculation
Currently mx53 (CortexA8) running at 1GHz reports: Calibrating delay loop... 663.55 BogoMIPS (lpj=3317760) Tom Evans verified that alignments of 0x0 and 0x8 run the two instructions of __loop_delay in one clock cycle (1 clock/loop), while alignments of 0x4 and 0xc take 3 clocks to run the loop twice. (1.5 clock/loop) The original object code looks like this: 00000010 <__loop_const_udelay>: 10: e3e01000 mvn r1, #0 14: e51f201c ldr r2, [pc, #-28] ; 0 <__loop_udelay-0x8> 18: e5922000 ldr r2, [r2] 1c: e0800921 add r0, r0, r1, lsr #18 20: e1a00720 lsr r0, r0, #14 24: e0822b21 add r2, r2, r1, lsr #22 28: e1a02522 lsr r2, r2, #10 2c: e0000092 mul r0, r2, r0 30: e0800d21 add r0, r0, r1, lsr #26 34: e1b00320 lsrs r0, r0, #6 38: 01a0f00e moveq pc, lr 0000003c <__loop_delay>: 3c: e2500001 subs r0, r0, #1 40: 8afffffe bhi 3c <__loop_delay> 44: e1a0f00e mov pc, lr After adding the 'align 3' directive to __loop_delay (align to 8 bytes): 00000010 <__loop_const_udelay>: 10: e3e01000 mvn r1, #0 14: e51f201c ldr r2, [pc, #-28] ; 0 <__loop_udelay-0x8> 18: e5922000 ldr r2, [r2] 1c: e0800921 add r0, r0, r1, lsr #18 20: e1a00720 lsr r0, r0, #14 24: e0822b21 add r2, r2, r1, lsr #22 28: e1a02522 lsr r2, r2, #10 2c: e0000092 mul r0, r2, r0 30: e0800d21 add r0, r0, r1, lsr #26 34: e1b00320 lsrs r0, r0, #6 38: 01a0f00e moveq pc, lr 3c: e320f000 nop {0} 00000040 <__loop_delay>: 40: e2500001 subs r0, r0, #1 44: 8afffffe bhi 40 <__loop_delay> 48: e1a0f00e mov pc, lr 4c: e320f000 nop {0} , which now reports: Calibrating delay loop... 996.14 BogoMIPS (lpj=4980736) Some more test results: On mx31 (ARM1136) running at 532 MHz, before the patch: Calibrating delay loop... 351.43 BogoMIPS (lpj=1757184) On mx31 (ARM1136) running at 532 MHz after the patch: Calibrating delay loop... 528.79 BogoMIPS (lpj=2643968) Also tested on mx6 (CortexA9) and on mx27 (ARM926), which shows the same BogoMIPS value before and after this patch. Reported-by: Tom Evans <tom_usenet@optusnet.com.au> Suggested-by: Tom Evans <tom_usenet@optusnet.com.au> Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm')
-rw-r--r--arch/arm/lib/delay-loop.S1
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/arm/lib/delay-loop.S b/arch/arm/lib/delay-loop.S
index 36b668d..bc1033b 100644
--- a/arch/arm/lib/delay-loop.S
+++ b/arch/arm/lib/delay-loop.S
@@ -40,6 +40,7 @@ ENTRY(__loop_const_udelay) @ 0 <= r0 <= 0x7fffff06
/*
* loops = r0 * HZ * loops_per_jiffy / 1000000
*/
+ .align 3
@ Delay routine
ENTRY(__loop_delay)
OpenPOWER on IntegriCloud