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| author | Fabio Estevam <festevam@gmail.com> | 2013-11-30 15:24:42 +0100 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2013-11-30 22:21:03 +0000 |
| commit | 11d4bb1bd067f9d01d18f620ccfad516dc579593 (patch) | |
| tree | abd79988692f334730e2c245a5bd8db56b46e03b /arch/arm/lib | |
| parent | e2ccba49085ab5d71b092de2a5176eb9b19cc876 (diff) | |
| download | lwn-11d4bb1bd067f9d01d18f620ccfad516dc579593.tar.gz lwn-11d4bb1bd067f9d01d18f620ccfad516dc579593.zip | |
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/lib')
| -rw-r--r-- | arch/arm/lib/delay-loop.S | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/arm/lib/delay-loop.S b/arch/arm/lib/delay-loop.S index 36b668d8e121..bc1033b897b4 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) |