[linux.git] / init / calibrate.c

// SPDX-License-Identifier: GPL-2.0
/* calibrate.c: default delay calibration
 *
 * Excised from init/main.c
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <linux/jiffies.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/timex.h>
#include <linux/smp.h>
#include <linux/percpu.h>

unsigned long lpj_fine;
unsigned long preset_lpj;
static int __init lpj_setup(char *str)
{
	preset_lpj = simple_strtoul(str,NULL,0);
	return 1;
}

__setup("lpj=", lpj_setup);

#ifdef ARCH_HAS_READ_CURRENT_TIMER

/* This routine uses the read_current_timer() routine and gets the
 * loops per jiffy directly, instead of guessing it using delay().
 * Also, this code tries to handle non-maskable asynchronous events
 * (like SMIs)
 */
#define DELAY_CALIBRATION_TICKS			((HZ < 100) ? 1 : (HZ/100))
#define MAX_DIRECT_CALIBRATION_RETRIES		5

static unsigned long calibrate_delay_direct(void)
{
	unsigned long pre_start, start, post_start;
	unsigned long pre_end, end, post_end;
	unsigned long start_jiffies;
	unsigned long timer_rate_min, timer_rate_max;
	unsigned long good_timer_sum = 0;
	unsigned long good_timer_count = 0;
	unsigned long measured_times[MAX_DIRECT_CALIBRATION_RETRIES];
	int max = -1; /* index of measured_times with max/min values or not set */
	int min = -1;
	int i;

	if (read_current_timer(&pre_start) < 0 )
		return 0;

	/*
	 * A simple loop like
	 *	while ( jiffies < start_jiffies+1)
	 *		start = read_current_timer();
	 * will not do. As we don't really know whether jiffy switch
	 * happened first or timer_value was read first. And some asynchronous
	 * event can happen between these two events introducing errors in lpj.
	 *
	 * So, we do
	 * 1. pre_start <- When we are sure that jiffy switch hasn't happened
	 * 2. check jiffy switch
	 * 3. start <- timer value before or after jiffy switch
	 * 4. post_start <- When we are sure that jiffy switch has happened
	 *
	 * Note, we don't know anything about order of 2 and 3.
	 * Now, by looking at post_start and pre_start difference, we can
	 * check whether any asynchronous event happened or not
	 */

	for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
		pre_start = 0;
		read_current_timer(&start);
		start_jiffies = jiffies;
		while (time_before_eq(jiffies, start_jiffies + 1)) {
			pre_start = start;
			read_current_timer(&start);
		}
		read_current_timer(&post_start);

		pre_end = 0;
		end = post_start;
		while (time_before_eq(jiffies, start_jiffies + 1 +
					       DELAY_CALIBRATION_TICKS)) {
			pre_end = end;
			read_current_timer(&end);
		}
		read_current_timer(&post_end);

		timer_rate_max = (post_end - pre_start) /
					DELAY_CALIBRATION_TICKS;
		timer_rate_min = (pre_end - post_start) /
					DELAY_CALIBRATION_TICKS;

		/*
		 * If the upper limit and lower limit of the timer_rate is
		 * >= 12.5% apart, redo calibration.
		 */
		if (start >= post_end)
			printk(KERN_NOTICE "calibrate_delay_direct() ignoring "
					"timer_rate as we had a TSC wrap around"
					" start=%lu >=post_end=%lu\n",
				start, post_end);
		if (start < post_end && pre_start != 0 && pre_end != 0 &&
		    (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
			good_timer_count++;
			good_timer_sum += timer_rate_max;
			measured_times[i] = timer_rate_max;
			if (max < 0 || timer_rate_max > measured_times[max])
				max = i;
			if (min < 0 || timer_rate_max < measured_times[min])
				min = i;
		} else
			measured_times[i] = 0;

	}

	/*
	 * Find the maximum & minimum - if they differ too much throw out the
	 * one with the largest difference from the mean and try again...
	 */
	while (good_timer_count > 1) {
		unsigned long estimate;
		unsigned long maxdiff;

		/* compute the estimate */
		estimate = (good_timer_sum/good_timer_count);
		maxdiff = estimate >> 3;

		/* if range is within 12% let's take it */
		if ((measured_times[max] - measured_times[min]) < maxdiff)
			return estimate;

		/* ok - drop the worse value and try again... */
		good_timer_sum = 0;
		good_timer_count = 0;
		if ((measured_times[max] - estimate) <
				(estimate - measured_times[min])) {
			printk(KERN_NOTICE "calibrate_delay_direct() dropping "
					"min bogoMips estimate %d = %lu\n",
				min, measured_times[min]);
			measured_times[min] = 0;
			min = max;
		} else {
			printk(KERN_NOTICE "calibrate_delay_direct() dropping "
					"max bogoMips estimate %d = %lu\n",
				max, measured_times[max]);
			measured_times[max] = 0;
			max = min;
		}

		for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
			if (measured_times[i] == 0)
				continue;
			good_timer_count++;
			good_timer_sum += measured_times[i];
			if (measured_times[i] < measured_times[min])
				min = i;
			if (measured_times[i] > measured_times[max])
				max = i;
		}

	}

	printk(KERN_NOTICE "calibrate_delay_direct() failed to get a good "
	       "estimate for loops_per_jiffy.\nProbably due to long platform "
		"interrupts. Consider using \"lpj=\" boot option.\n");
	return 0;
}
#else
static unsigned long calibrate_delay_direct(void)
{
	return 0;
}
#endif

/*
 * This is the number of bits of precision for the loops_per_jiffy.  Each
 * time we refine our estimate after the first takes 1.5/HZ seconds, so try
 * to start with a good estimate.
 * For the boot cpu we can skip the delay calibration and assign it a value
 * calculated based on the timer frequency.
 * For the rest of the CPUs we cannot assume that the timer frequency is same as
 * the cpu frequency, hence do the calibration for those.
 */
#define LPS_PREC 8

static unsigned long calibrate_delay_converge(void)
{
	/* First stage - slowly accelerate to find initial bounds */
	unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
	int trials = 0, band = 0, trial_in_band = 0;

	lpj = (1<<12);

	/* wait for "start of" clock tick */
	ticks = jiffies;
	while (ticks == jiffies)
		; /* nothing */
	/* Go .. */
	ticks = jiffies;
	do {
		if (++trial_in_band == (1<<band)) {
			++band;
			trial_in_band = 0;
		}
		__delay(lpj * band);
		trials += band;
	} while (ticks == jiffies);
	/*
	 * We overshot, so retreat to a clear underestimate. Then estimate
	 * the largest likely undershoot. This defines our chop bounds.
	 */
	trials -= band;
	loopadd_base = lpj * band;
	lpj_base = lpj * trials;

recalibrate:
	lpj = lpj_base;
	loopadd = loopadd_base;

	/*
	 * Do a binary approximation to get lpj set to
	 * equal one clock (up to LPS_PREC bits)
	 */
	chop_limit = lpj >> LPS_PREC;
	while (loopadd > chop_limit) {
		lpj += loopadd;
		ticks = jiffies;
		while (ticks == jiffies)
			; /* nothing */
		ticks = jiffies;
		__delay(lpj);
		if (jiffies != ticks)	/* longer than 1 tick */
			lpj -= loopadd;
		loopadd >>= 1;
	}
	/*
	 * If we incremented every single time possible, presume we've
	 * massively underestimated initially, and retry with a higher
	 * start, and larger range. (Only seen on x86_64, due to SMIs)
	 */
	if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
		lpj_base = lpj;
		loopadd_base <<= 2;
		goto recalibrate;
	}

	return lpj;
}

static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 };

/*
 * Check if cpu calibration delay is already known. For example,
 * some processors with multi-core sockets may have all cores
 * with the same calibration delay.
 *
 * Architectures should override this function if a faster calibration
 * method is available.
 */
unsigned long __attribute__((weak)) calibrate_delay_is_known(void)
{
	return 0;
}

/*
 * Indicate the cpu delay calibration is done. This can be used by
 * architectures to stop accepting delay timer registrations after this point.
 */

void __attribute__((weak)) calibration_delay_done(void)
{
}

void calibrate_delay(void)
{
	unsigned long lpj;
	static bool printed;
	int this_cpu = smp_processor_id();

	if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
		lpj = per_cpu(cpu_loops_per_jiffy, this_cpu);
		if (!printed)
			pr_info("Calibrating delay loop (skipped) "
				"already calibrated this CPU");
	} else if (preset_lpj) {
		lpj = preset_lpj;
		if (!printed)
			pr_info("Calibrating delay loop (skipped) "
				"preset value.. ");
	} else if ((!printed) && lpj_fine) {
		lpj = lpj_fine;
		pr_info("Calibrating delay loop (skipped), "
			"value calculated using timer frequency.. ");
	} else if ((lpj = calibrate_delay_is_known())) {
		;
	} else if ((lpj = calibrate_delay_direct()) != 0) {
		if (!printed)
			pr_info("Calibrating delay using timer "
				"specific routine.. ");
	} else {
		if (!printed)
			pr_info("Calibrating delay loop... ");
		lpj = calibrate_delay_converge();
	}
	per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj;
	if (!printed)
		pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
			lpj/(500000/HZ),
			(lpj/(5000/HZ)) % 100, lpj);

	loops_per_jiffy = lpj;
	printed = true;

	calibration_delay_done();
}
Commit	Line	Data
b2441318	1	// SPDX-License-Identifier: GPL-2.0
1da177e4 LT	2	/* calibrate.c: default delay calibration
	3	*
	4	* Excised from init/main.c
	5	* Copyright (C) 1991, 1992 Linus Torvalds
	6	*/
	7
cd354f1a	8	#include <linux/jiffies.h>
1da177e4 LT	9	#include <linux/delay.h>
1da177e4 LT	10	#include <linux/init.h>
941e492b	11	#include <linux/timex.h>
3da757da	12	#include <linux/smp.h>
7afe1845	13	#include <linux/percpu.h>
8a9e1b0f	14
f3f3149f	15	unsigned long lpj_fine;
bfe8df3d	16	unsigned long preset_lpj;
1da177e4 LT	17	static int __init lpj_setup(char *str)
	18	{
	19	preset_lpj = simple_strtoul(str,NULL,0);
	20	return 1;
	21	}
	22
	23	__setup("lpj=", lpj_setup);
	24
8a9e1b0f VP	25	#ifdef ARCH_HAS_READ_CURRENT_TIMER
	26
	27	/* This routine uses the read_current_timer() routine and gets the
	28	* loops per jiffy directly, instead of guessing it using delay().
	29	* Also, this code tries to handle non-maskable asynchronous events
	30	* (like SMIs)
	31	*/
	32	#define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100))
	33	#define MAX_DIRECT_CALIBRATION_RETRIES 5
	34
0db0628d	35	static unsigned long calibrate_delay_direct(void)
8a9e1b0f VP	36	{
	37	unsigned long pre_start, start, post_start;
	38	unsigned long pre_end, end, post_end;
	39	unsigned long start_jiffies;
f3f3149f AK	40	unsigned long timer_rate_min, timer_rate_max;
	41	unsigned long good_timer_sum = 0;
	42	unsigned long good_timer_count = 0;
d2b46313 AW	43	unsigned long measured_times[MAX_DIRECT_CALIBRATION_RETRIES];
	44	int max = -1; /* index of measured_times with max/min values or not set */
	45	int min = -1;
8a9e1b0f VP	46	int i;
	47
	48	if (read_current_timer(&pre_start) < 0 )
	49	return 0;
	50
	51	/*
	52	* A simple loop like
	53	* while ( jiffies < start_jiffies+1)
	54	* start = read_current_timer();
	55	* will not do. As we don't really know whether jiffy switch
	56	* happened first or timer_value was read first. And some asynchronous
	57	* event can happen between these two events introducing errors in lpj.
	58	*
	59	* So, we do
	60	* 1. pre_start <- When we are sure that jiffy switch hasn't happened
	61	* 2. check jiffy switch
	62	* 3. start <- timer value before or after jiffy switch
	63	* 4. post_start <- When we are sure that jiffy switch has happened
	64	*
	65	* Note, we don't know anything about order of 2 and 3.
	66	* Now, by looking at post_start and pre_start difference, we can
	67	* check whether any asynchronous event happened or not
	68	*/
	69
	70	for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
	71	pre_start = 0;
	72	read_current_timer(&start);
	73	start_jiffies = jiffies;
70a06228	74	while (time_before_eq(jiffies, start_jiffies + 1)) {
8a9e1b0f VP	75	pre_start = start;
	76	read_current_timer(&start);
	77	}
	78	read_current_timer(&post_start);
	79
	80	pre_end = 0;
	81	end = post_start;
70a06228 TD	82	while (time_before_eq(jiffies, start_jiffies + 1 +
70a06228 TD	83	DELAY_CALIBRATION_TICKS)) {
8a9e1b0f VP	84	pre_end = end;
	85	read_current_timer(&end);
	86	}
	87	read_current_timer(&post_end);
	88
f3f3149f AK	89	timer_rate_max = (post_end - pre_start) /
	90	DELAY_CALIBRATION_TICKS;
	91	timer_rate_min = (pre_end - post_start) /
	92	DELAY_CALIBRATION_TICKS;
8a9e1b0f VP	93
8a9e1b0f VP	94	/*
f3f3149f	95	* If the upper limit and lower limit of the timer_rate is
8a9e1b0f VP	96	* >= 12.5% apart, redo calibration.
8a9e1b0f VP	97	*/
d2b46313 AW	98	if (start >= post_end)
	99	printk(KERN_NOTICE "calibrate_delay_direct() ignoring "
	100	"timer_rate as we had a TSC wrap around"
	101	" start=%lu >=post_end=%lu\n",
	102	start, post_end);
	103	if (start < post_end && pre_start != 0 && pre_end != 0 &&
f3f3149f AK	104	(timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
	105	good_timer_count++;
	106	good_timer_sum += timer_rate_max;
d2b46313 AW	107	measured_times[i] = timer_rate_max;
	108	if (max < 0 \|\| timer_rate_max > measured_times[max])
	109	max = i;
	110	if (min < 0 \|\| timer_rate_max < measured_times[min])
	111	min = i;
	112	} else
	113	measured_times[i] = 0;
	114
8a9e1b0f VP	115	}
8a9e1b0f VP	116
d2b46313 AW	117	/*
	118	* Find the maximum & minimum - if they differ too much throw out the
	119	* one with the largest difference from the mean and try again...
	120	*/
	121	while (good_timer_count > 1) {
	122	unsigned long estimate;
	123	unsigned long maxdiff;
	124
	125	/* compute the estimate */
	126	estimate = (good_timer_sum/good_timer_count);
	127	maxdiff = estimate >> 3;
	128
	129	/* if range is within 12% let's take it */
	130	if ((measured_times[max] - measured_times[min]) < maxdiff)
	131	return estimate;
	132
	133	/* ok - drop the worse value and try again... */
	134	good_timer_sum = 0;
	135	good_timer_count = 0;
	136	if ((measured_times[max] - estimate) <
	137	(estimate - measured_times[min])) {
	138	printk(KERN_NOTICE "calibrate_delay_direct() dropping "
	139	"min bogoMips estimate %d = %lu\n",
	140	min, measured_times[min]);
	141	measured_times[min] = 0;
	142	min = max;
	143	} else {
	144	printk(KERN_NOTICE "calibrate_delay_direct() dropping "
	145	"max bogoMips estimate %d = %lu\n",
	146	max, measured_times[max]);
	147	measured_times[max] = 0;
	148	max = min;
	149	}
	150
	151	for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
	152	if (measured_times[i] == 0)
	153	continue;
	154	good_timer_count++;
	155	good_timer_sum += measured_times[i];
	156	if (measured_times[i] < measured_times[min])
	157	min = i;
	158	if (measured_times[i] > measured_times[max])
	159	max = i;
	160	}
	161
	162	}
8a9e1b0f	163
d2b46313 AW	164	printk(KERN_NOTICE "calibrate_delay_direct() failed to get a good "
	165	"estimate for loops_per_jiffy.\nProbably due to long platform "
	166	"interrupts. Consider using \"lpj=\" boot option.\n");
8a9e1b0f VP	167	return 0;
	168	}
	169	#else
0db0628d PG	170	static unsigned long calibrate_delay_direct(void)
	171	{
	172	return 0;
	173	}
8a9e1b0f VP	174	#endif
8a9e1b0f VP	175
1da177e4 LT	176	/*
1da177e4 LT	177	* This is the number of bits of precision for the loops_per_jiffy. Each
191e5688 PC	178	* time we refine our estimate after the first takes 1.5/HZ seconds, so try
191e5688 PC	179	* to start with a good estimate.
3da757da	180	* For the boot cpu we can skip the delay calibration and assign it a value
f3f3149f AK	181	* calculated based on the timer frequency.
f3f3149f AK	182	* For the rest of the CPUs we cannot assume that the timer frequency is same as
3da757da	183	* the cpu frequency, hence do the calibration for those.
1da177e4 LT	184	*/
	185	#define LPS_PREC 8
	186
0db0628d	187	static unsigned long calibrate_delay_converge(void)
1da177e4	188	{
191e5688	189	/* First stage - slowly accelerate to find initial bounds */
b1b5f65e	190	unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
191e5688	191	int trials = 0, band = 0, trial_in_band = 0;
71c696b1 PC	192
71c696b1 PC	193	lpj = (1<<12);
191e5688 PC	194
	195	/* wait for "start of" clock tick */
	196	ticks = jiffies;
	197	while (ticks == jiffies)
	198	; /* nothing */
	199	/* Go .. */
	200	ticks = jiffies;
	201	do {
	202	if (++trial_in_band == (1<<band)) {
	203	++band;
	204	trial_in_band = 0;
	205	}
	206	__delay(lpj * band);
	207	trials += band;
	208	} while (ticks == jiffies);
	209	/*
	210	* We overshot, so retreat to a clear underestimate. Then estimate
	211	* the largest likely undershoot. This defines our chop bounds.
	212	*/
	213	trials -= band;
b1b5f65e PC	214	loopadd_base = lpj * band;
	215	lpj_base = lpj * trials;
	216
	217	recalibrate:
	218	lpj = lpj_base;
	219	loopadd = loopadd_base;
71c696b1 PC	220
	221	/*
	222	* Do a binary approximation to get lpj set to
191e5688	223	* equal one clock (up to LPS_PREC bits)
71c696b1	224	*/
b1b5f65e	225	chop_limit = lpj >> LPS_PREC;
191e5688 PC	226	while (loopadd > chop_limit) {
191e5688 PC	227	lpj += loopadd;
71c696b1 PC	228	ticks = jiffies;
71c696b1 PC	229	while (ticks == jiffies)
191e5688	230	; /* nothing */
71c696b1 PC	231	ticks = jiffies;
	232	__delay(lpj);
	233	if (jiffies != ticks) /* longer than 1 tick */
191e5688 PC	234	lpj -= loopadd;
191e5688 PC	235	loopadd >>= 1;
71c696b1	236	}
b1b5f65e PC	237	/*
	238	* If we incremented every single time possible, presume we've
	239	* massively underestimated initially, and retry with a higher
	240	* start, and larger range. (Only seen on x86_64, due to SMIs)
	241	*/
	242	if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
	243	lpj_base = lpj;
	244	loopadd_base <<= 2;
	245	goto recalibrate;
	246	}
71c696b1 PC	247
	248	return lpj;
	249	}
	250
7afe1845 SN	251	static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 };
7afe1845 SN	252
b565201c JS	253	/*
	254	* Check if cpu calibration delay is already known. For example,
	255	* some processors with multi-core sockets may have all cores
	256	* with the same calibration delay.
	257	*
	258	* Architectures should override this function if a faster calibration
	259	* method is available.
	260	*/
0db0628d	261	unsigned long __attribute__((weak)) calibrate_delay_is_known(void)
b565201c JS	262	{
	263	return 0;
	264	}
	265
e6639117 PDS	266	/*
	267	* Indicate the cpu delay calibration is done. This can be used by
	268	* architectures to stop accepting delay timer registrations after this point.
	269	*/
	270
	271	void __attribute__((weak)) calibration_delay_done(void)
	272	{
	273	}
	274
0db0628d	275	void calibrate_delay(void)
71c696b1	276	{
1b19ca9f	277	unsigned long lpj;
feae3203	278	static bool printed;
7afe1845	279	int this_cpu = smp_processor_id();
1da177e4	280
7afe1845 SN	281	if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
7afe1845 SN	282	lpj = per_cpu(cpu_loops_per_jiffy, this_cpu);
8595c539 DT	283	if (!printed)
8595c539 DT	284	pr_info("Calibrating delay loop (skipped) "
7afe1845 SN	285	"already calibrated this CPU");
7afe1845 SN	286	} else if (preset_lpj) {
1b19ca9f	287	lpj = preset_lpj;
feae3203 MT	288	if (!printed)
	289	pr_info("Calibrating delay loop (skipped) "
	290	"preset value.. ");
	291	} else if ((!printed) && lpj_fine) {
1b19ca9f	292	lpj = lpj_fine;
feae3203	293	pr_info("Calibrating delay loop (skipped), "
f3f3149f	294	"value calculated using timer frequency.. ");
b565201c JS	295	} else if ((lpj = calibrate_delay_is_known())) {
b565201c JS	296	;
1b19ca9f	297	} else if ((lpj = calibrate_delay_direct()) != 0) {
feae3203 MT	298	if (!printed)
	299	pr_info("Calibrating delay using timer "
	300	"specific routine.. ");
1da177e4	301	} else {
feae3203 MT	302	if (!printed)
feae3203 MT	303	pr_info("Calibrating delay loop... ");
1b19ca9f	304	lpj = calibrate_delay_converge();
1da177e4	305	}
7afe1845	306	per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj;
feae3203 MT	307	if (!printed)
feae3203 MT	308	pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
1b19ca9f RK	309	lpj/(500000/HZ),
1b19ca9f RK	310	(lpj/(5000/HZ)) % 100, lpj);
feae3203	311
1b19ca9f	312	loops_per_jiffy = lpj;
feae3203	313	printed = true;
e6639117 PDS	314
e6639117 PDS	315	calibration_delay_done();
1da177e4	316	}