lkml.org 
[lkml]   [2013]   [Mar]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectIn SMP, every CPU has its own loops_per_jiffy value, __loop_const_udelay time period is not right if two cpus are running in different frequency.
From
in __loop_const_udelay function, the delayed time period is calculated
according to loops_per_jiffy.
In SMP, every CPU has its own loops_per_jiffy value,
__loop_const_udelay time period is not right if two cpus are running
in different frequency.


the following is file arch/arm/lib/delay-loop.S
/*
* linux/arch/arm/lib/delay.S
*
* Copyright (C) 1995, 1996 Russell King
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/linkage.h>
#include <asm/assembler.h>
#include <asm/delay.h>
.text

.LC0: .word loops_per_jiffy
.LC1: .word UDELAY_MULT

/*
* r0 <= 2000
* lpj <= 0x01ffffff (max. 3355 bogomips)
* HZ <= 1000
*/

ENTRY(__loop_udelay)
ldr r2, .LC1
mul r0, r2, r0
ENTRY(__loop_const_udelay) @ 0 <= r0 <= 0x7fffff06
mov r1, #-1
ldr r2, .LC0
ldr r2, [r2] @ max = 0x01ffffff
add r0, r0, r1, lsr #32-14
mov r0, r0, lsr #14 @ max = 0x0001ffff
add r2, r2, r1, lsr #32-10
mov r2, r2, lsr #10 @ max = 0x00007fff
mul r0, r2, r0 @ max = 2^32-1
add r0, r0, r1, lsr #32-6
movs r0, r0, lsr #6
moveq pc, lr

/*
* loops = r0 * HZ * loops_per_jiffy / 1000000
*/

@ Delay routine
ENTRY(__loop_delay)
subs r0, r0, #1
#if 0
movls pc, lr
subs r0, r0, #1
movls pc, lr
subs r0, r0, #1
movls pc, lr
subs r0, r0, #1
movls pc, lr
subs r0, r0, #1
movls pc, lr
subs r0, r0, #1
movls pc, lr
subs r0, r0, #1
movls pc, lr
subs r0, r0, #1
#endif
bhi __loop_delay
mov pc, lr
ENDPROC(__loop_udelay)
ENDPROC(__loop_const_udelay)
ENDPROC(__loop_delay)


\
 
 \ /
  Last update: 2013-03-14 16:43    [W:0.027 / U:0.108 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site