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>
141 lines
2.8 KiB
C
141 lines
2.8 KiB
C
/*
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* Precise Delay Loops for i386
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*
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* Copyright (C) 1993 Linus Torvalds
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* Copyright (C) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
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* Copyright (C) 2008 Jiri Hladky <hladky _dot_ jiri _at_ gmail _dot_ com>
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*
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* The __delay function must _NOT_ be inlined as its execution time
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* depends wildly on alignment on many x86 processors. The additional
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* jump magic is needed to get the timing stable on all the CPU's
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* we have to worry about.
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*/
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#include <linux/module.h>
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#include <linux/sched.h>
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#include <linux/timex.h>
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#include <linux/preempt.h>
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#include <linux/delay.h>
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#include <linux/init.h>
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#include <asm/processor.h>
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#include <asm/delay.h>
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#include <asm/timer.h>
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#ifdef CONFIG_SMP
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# include <asm/smp.h>
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#endif
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/* simple loop based delay: */
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static void delay_loop(unsigned long loops)
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{
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asm volatile(
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" test %0,%0 \n"
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" jz 3f \n"
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" jmp 1f \n"
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".align 16 \n"
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"1: jmp 2f \n"
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".align 16 \n"
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"2: dec %0 \n"
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" jnz 2b \n"
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"3: dec %0 \n"
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: /* we don't need output */
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:"a" (loops)
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);
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}
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/* TSC based delay: */
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static void delay_tsc(unsigned long loops)
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{
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unsigned long bclock, now;
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int cpu;
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preempt_disable();
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cpu = smp_processor_id();
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rdtsc_barrier();
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rdtscl(bclock);
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for (;;) {
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rdtsc_barrier();
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rdtscl(now);
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if ((now - bclock) >= loops)
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break;
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/* Allow RT tasks to run */
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preempt_enable();
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rep_nop();
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preempt_disable();
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/*
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* It is possible that we moved to another CPU, and
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* since TSC's are per-cpu we need to calculate
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* that. The delay must guarantee that we wait "at
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* least" the amount of time. Being moved to another
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* CPU could make the wait longer but we just need to
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* make sure we waited long enough. Rebalance the
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* counter for this CPU.
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*/
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if (unlikely(cpu != smp_processor_id())) {
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loops -= (now - bclock);
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cpu = smp_processor_id();
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rdtsc_barrier();
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rdtscl(bclock);
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}
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}
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preempt_enable();
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}
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/*
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* Since we calibrate only once at boot, this
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* function should be set once at boot and not changed
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*/
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static void (*delay_fn)(unsigned long) = delay_loop;
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void use_tsc_delay(void)
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{
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delay_fn = delay_tsc;
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}
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int __devinit read_current_timer(unsigned long *timer_val)
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{
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if (delay_fn == delay_tsc) {
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rdtscll(*timer_val);
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return 0;
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}
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return -1;
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}
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void __delay(unsigned long loops)
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{
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delay_fn(loops);
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}
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EXPORT_SYMBOL(__delay);
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inline void __const_udelay(unsigned long xloops)
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{
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int d0;
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xloops *= 4;
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asm("mull %%edx"
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:"=d" (xloops), "=&a" (d0)
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:"1" (xloops), "0"
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(cpu_data(raw_smp_processor_id()).loops_per_jiffy * (HZ/4)));
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__delay(++xloops);
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}
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EXPORT_SYMBOL(__const_udelay);
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void __udelay(unsigned long usecs)
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{
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__const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
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}
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EXPORT_SYMBOL(__udelay);
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void __ndelay(unsigned long nsecs)
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{
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__const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
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}
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EXPORT_SYMBOL(__ndelay);
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