e888d7facd
delay_tsc needs rdtsc_barrier to provide proper delay. Output from a test driver using hpet to cross check delay provided by udelay(). Before: [ 86.794363] Expected delay 5us actual 4679ns [ 87.154362] Expected delay 5us actual 698ns [ 87.514162] Expected delay 5us actual 4539ns [ 88.653716] Expected delay 5us actual 4539ns [ 94.664106] Expected delay 10us actual 9638ns [ 95.049351] Expected delay 10us actual 10126ns [ 95.416110] Expected delay 10us actual 9568ns [ 95.799216] Expected delay 10us actual 9638ns [ 103.624104] Expected delay 10us actual 9707ns [ 104.020619] Expected delay 10us actual 768ns [ 104.419951] Expected delay 10us actual 9707ns After: [ 50.983320] Expected delay 5us actual 5587ns [ 51.261807] Expected delay 5us actual 5587ns [ 51.565715] Expected delay 5us actual 5657ns [ 51.861171] Expected delay 5us actual 5587ns [ 52.164704] Expected delay 5us actual 5726ns [ 52.487457] Expected delay 5us actual 5657ns [ 52.789338] Expected delay 5us actual 5726ns [ 57.119680] Expected delay 10us actual 10755ns [ 57.893997] Expected delay 10us actual 10615ns [ 58.261287] Expected delay 10us actual 10755ns [ 58.620505] Expected delay 10us actual 10825ns [ 58.941035] Expected delay 10us actual 10755ns [ 59.320903] Expected delay 10us actual 10615ns [ 61.306311] Expected delay 10us actual 10755ns [ 61.520542] Expected delay 10us actual 10615ns Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
140 lines
2.8 KiB
C
140 lines
2.8 KiB
C
/*
|
|
* Precise Delay Loops for i386
|
|
*
|
|
* Copyright (C) 1993 Linus Torvalds
|
|
* Copyright (C) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
|
|
* Copyright (C) 2008 Jiri Hladky <hladky _dot_ jiri _at_ gmail _dot_ com>
|
|
*
|
|
* The __delay function must _NOT_ be inlined as its execution time
|
|
* depends wildly on alignment on many x86 processors. The additional
|
|
* jump magic is needed to get the timing stable on all the CPU's
|
|
* we have to worry about.
|
|
*/
|
|
|
|
#include <linux/module.h>
|
|
#include <linux/sched.h>
|
|
#include <linux/timex.h>
|
|
#include <linux/preempt.h>
|
|
#include <linux/delay.h>
|
|
#include <linux/init.h>
|
|
|
|
#include <asm/processor.h>
|
|
#include <asm/delay.h>
|
|
#include <asm/timer.h>
|
|
|
|
#ifdef CONFIG_SMP
|
|
# include <asm/smp.h>
|
|
#endif
|
|
|
|
/* simple loop based delay: */
|
|
static void delay_loop(unsigned long loops)
|
|
{
|
|
asm volatile(
|
|
" test %0,%0 \n"
|
|
" jz 3f \n"
|
|
" jmp 1f \n"
|
|
|
|
".align 16 \n"
|
|
"1: jmp 2f \n"
|
|
|
|
".align 16 \n"
|
|
"2: dec %0 \n"
|
|
" jnz 2b \n"
|
|
"3: dec %0 \n"
|
|
|
|
: /* we don't need output */
|
|
:"a" (loops)
|
|
);
|
|
}
|
|
|
|
/* TSC based delay: */
|
|
static void delay_tsc(unsigned long loops)
|
|
{
|
|
unsigned long bclock, now;
|
|
int cpu;
|
|
|
|
preempt_disable();
|
|
cpu = smp_processor_id();
|
|
rdtsc_barrier();
|
|
rdtscl(bclock);
|
|
for (;;) {
|
|
rdtsc_barrier();
|
|
rdtscl(now);
|
|
if ((now - bclock) >= loops)
|
|
break;
|
|
|
|
/* Allow RT tasks to run */
|
|
preempt_enable();
|
|
rep_nop();
|
|
preempt_disable();
|
|
|
|
/*
|
|
* It is possible that we moved to another CPU, and
|
|
* since TSC's are per-cpu we need to calculate
|
|
* that. The delay must guarantee that we wait "at
|
|
* least" the amount of time. Being moved to another
|
|
* CPU could make the wait longer but we just need to
|
|
* make sure we waited long enough. Rebalance the
|
|
* counter for this CPU.
|
|
*/
|
|
if (unlikely(cpu != smp_processor_id())) {
|
|
loops -= (now - bclock);
|
|
cpu = smp_processor_id();
|
|
rdtsc_barrier();
|
|
rdtscl(bclock);
|
|
}
|
|
}
|
|
preempt_enable();
|
|
}
|
|
|
|
/*
|
|
* Since we calibrate only once at boot, this
|
|
* function should be set once at boot and not changed
|
|
*/
|
|
static void (*delay_fn)(unsigned long) = delay_loop;
|
|
|
|
void use_tsc_delay(void)
|
|
{
|
|
delay_fn = delay_tsc;
|
|
}
|
|
|
|
int __devinit read_current_timer(unsigned long *timer_val)
|
|
{
|
|
if (delay_fn == delay_tsc) {
|
|
rdtscll(*timer_val);
|
|
return 0;
|
|
}
|
|
return -1;
|
|
}
|
|
|
|
void __delay(unsigned long loops)
|
|
{
|
|
delay_fn(loops);
|
|
}
|
|
EXPORT_SYMBOL(__delay);
|
|
|
|
inline void __const_udelay(unsigned long xloops)
|
|
{
|
|
int d0;
|
|
|
|
xloops *= 4;
|
|
asm("mull %%edx"
|
|
:"=d" (xloops), "=&a" (d0)
|
|
:"1" (xloops), "0"
|
|
(cpu_data(raw_smp_processor_id()).loops_per_jiffy * (HZ/4)));
|
|
|
|
__delay(++xloops);
|
|
}
|
|
EXPORT_SYMBOL(__const_udelay);
|
|
|
|
void __udelay(unsigned long usecs)
|
|
{
|
|
__const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
|
|
}
|
|
EXPORT_SYMBOL(__udelay);
|
|
|
|
void __ndelay(unsigned long nsecs)
|
|
{
|
|
__const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
|
|
}
|
|
EXPORT_SYMBOL(__ndelay);
|