Release 4.14 arch/x86/lib/delay.c

// SPDX-License-Identifier: GPL-2.0
/*
 *      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/export.h>
#include <linux/sched.h>
#include <linux/timex.h>
#include <linux/preempt.h>
#include <linux/delay.h>

#include <asm/processor.h>
#include <asm/delay.h>
#include <asm/timer.h>
#include <asm/mwait.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)
        );
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
John Stultz
10
66.67%
1
25.00%
Glauber de Oliveira Costa
3
20.00%
2
50.00%
Jiri Hladky
2
13.33%
1
25.00%
Total
15
100.00%
4
100.00%

/* TSC based delay: */


static void delay_tsc(unsigned long __loops)
{
	u64 bclock, now, loops = __loops;
	int cpu;

	preempt_disable();
	cpu = smp_processor_id();
	bclock = rdtsc_ordered();
	for (;;) {
		now = rdtsc_ordered();
		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();
			bclock = rdtsc_ordered();
		}
	}
	preempt_enable();
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
Steven Rostedt
55
53.92%
1
16.67%
John Stultz
26
25.49%
1
16.67%
Andrew Lutomirski
10
9.80%
2
33.33%
Andrew Morton
6
5.88%
1
16.67%
Thomas Gleixner
5
4.90%
1
16.67%
Total
102
100.00%
6
100.00%

/*
 * On some AMD platforms, MWAITX has a configurable 32-bit timer, that
 * counts with TSC frequency. The input value is the loop of the
 * counter, it will exit when the timer expires.
 */


static void delay_mwaitx(unsigned long __loops)
{
	u64 start, end, delay, loops = __loops;

	/*
         * Timer value of 0 causes MWAITX to wait indefinitely, unless there
         * is a store on the memory monitored by MONITORX.
         */
	if (loops == 0)
		return;

	start = rdtsc_ordered();

	for (;;) {
		delay = min_t(u64, MWAITX_MAX_LOOPS, loops);

		/*
                 * Use cpu_tss as a cacheline-aligned, seldomly
                 * accessed per-cpu variable as the monitor target.
                 */
		__monitorx(raw_cpu_ptr(&cpu_tss), 0, 0);

		/*
                 * AMD, like Intel, supports the EAX hint and EAX=0xf
                 * means, do not enter any deep C-state and we use it
                 * here in delay() to minimize wakeup latency.
                 */
		__mwaitx(MWAITX_DISABLE_CSTATES, delay, MWAITX_ECX_TIMER_ENABLE);

		end = rdtsc_ordered();

		if (loops <= end - start)
			break;

		loops -= end - start;

		start = end;
	}
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
Huang Rui
91
91.00%
1
33.33%
Janakarajan Natarajan
8
8.00%
1
33.33%
Borislav Petkov
1
1.00%
1
33.33%
Total
100
100.00%
3
100.00%

/*
 * 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)
{
	if (delay_fn == delay_loop)
		delay_fn = delay_tsc;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
John Stultz
11
64.71%
1
50.00%
Huang Rui
6
35.29%
1
50.00%
Total
17
100.00%
2
100.00%



void use_mwaitx_delay(void)
{
	delay_fn = delay_mwaitx;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
Huang Rui
11
100.00%
1
100.00%
Total
11
100.00%
1
100.00%



int read_current_timer(unsigned long *timer_val)
{
	if (delay_fn == delay_tsc) {
		*timer_val = rdtsc();
		return 0;
	}
	return -1;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
John Stultz
28
90.32%
1
33.33%
Andrew Lutomirski
3
9.68%
2
66.67%
Total
31
100.00%
3
100.00%



void __delay(unsigned long loops)
{
	delay_fn(loops);
}
Contributors
Person
Tokens
Prop
Commits
CommitProp
Linus Torvalds (pre-git)
13
92.86%
1
50.00%
John Stultz
1
7.14%
1
50.00%
Total
14
100.00%
2
100.00%


EXPORT_SYMBOL(__delay);



inline void __const_udelay(unsigned long xloops)
{
	unsigned long lpj = this_cpu_read(cpu_info.loops_per_jiffy) ? : loops_per_jiffy;
	int d0;

	xloops *= 4;
	asm("mull %%edx"
                :"=d" (xloops), "=&a" (d0)
                :"1" (xloops), "0" (lpj * (HZ / 4)));

	__delay(++xloops);
}
Contributors
Person
Tokens
Prop
Commits
CommitProp
Linus Torvalds (pre-git)
18
47.37%
2
40.00%
Jiri Slaby
15
39.47%
1
20.00%
Dominik Brodowski
5
13.16%
2
40.00%
Total
38
100.00%
5
100.00%


EXPORT_SYMBOL(__const_udelay);



void __udelay(unsigned long usecs)
{
	__const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
}
Contributors
Person
Tokens
Prop
Commits
CommitProp
Linus Torvalds (pre-git)
15
88.24%
1
50.00%
Dominik Brodowski
2
11.76%
1
50.00%
Total
17
100.00%
2
100.00%


EXPORT_SYMBOL(__udelay);



void __ndelay(unsigned long nsecs)
{
	__const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
}
Contributors
Person
Tokens
Prop
Commits
CommitProp
Alan Cox
17
100.00%
1
100.00%
Total
17
100.00%
1
100.00%


EXPORT_SYMBOL(__ndelay);
Overall Contributors
Person
Tokens
Prop
Commits
CommitProp
Huang Rui
112
25.69%
1
3.45%
John Stultz
97
22.25%
2
6.90%
Linus Torvalds (pre-git)
61
13.99%
4
13.79%
Steven Rostedt
55
12.61%
1
3.45%
Glauber de Oliveira Costa
18
4.13%
2
6.90%
Alan Cox
17
3.90%
1
3.45%
Jiri Slaby
15
3.44%
1
3.45%
Andrew Lutomirski
13
2.98%
4
13.79%
Andrew Morton
12
2.75%
2
6.90%
Janakarajan Natarajan
8
1.83%
1
3.45%
Alexey Dobriyan
7
1.61%
1
3.45%
Dominik Brodowski
7
1.61%
3
10.34%
Thomas Gleixner
5
1.15%
1
3.45%
Jiri Hladky
3
0.69%
1
3.45%
Linus Torvalds
3
0.69%
1
3.45%
Greg Kroah-Hartman
1
0.23%
1
3.45%
Paul Gortmaker
1
0.23%
1
3.45%
Borislav Petkov
1
0.23%
1
3.45%
Total
436
100.00%
29
100.00%
Directory: arch/x86/lib

Information contained on this website is for historical information purposes only and does not indicate or represent copyright ownership.