Documentation/scheduler/sched-pelt.c

/*
 * The following program is used to generate the constants for
 * computing sched averages.
 *
 * ==============================================================
 *		C program (compile with -lm)
 * ==============================================================
 */

#include <math.h>
#include <stdio.h>

#define HALFLIFE { 32, 16, 8 }
#define SHIFT 32

double y;

void calc_runnable_avg_yN_inv(const int halflife)
{
	int i;
	unsigned int x;

	printf("static const u32 runnable_avg_yN_inv[] = {");
	for (i = 0; i < halflife; i++) {
		x = ((1UL<<32)-1)*pow(y, i);

		if (i % 4 == 0) printf("\n\t");
		printf("0x%8x,", x);
	}
	printf("\n};\n\n");
}

int sum;

void calc_runnable_avg_yN_sum(const int halflife)
{
	int i;

	printf("static const u32 runnable_avg_yN_sum[] = {\n\t    0,");
	for (i = 1; i <= halflife; i++) {
		if (i == 1)
			sum *= y;
		else
			sum = sum*y + 1024*y;

		if (i % 11 == 0)
			printf("\n\t");

		printf("%5d,", sum);
	}
	printf("\n};\n\n");
}

int n;
long max;

void calc_converged_max(const int halflife)
{
	long last = 0, y_inv = ((1UL<<32)-1)*y;

	for (; ; n++) {
		if (n > -1)
			max = ((max*y_inv)>>SHIFT) + 1024;
			/*
			 * This is the same as:
			 * max = max*y + 1024;
			 */

		if (last == max)
			break;

		last = max;
	}
	n--;
	printf("#define LOAD_AVG_PERIOD %d\n", halflife);
	printf("#define LOAD_AVG_MAX %ld\n", max);
	printf("#define LOAD_AVG_MAX_N %d\n\n", n);
}

void calc_accumulated_sum_32(const int halflife)
{
	int i, x = sum;

	printf("static const u32 __accumulated_sum_N32[] = {\n\t     0,");
	for (i = 1; i <= n/halflife+1; i++) {
		if (i > 1)
			x = x/2 + sum;

		if (i % 6 == 0)
			printf("\n\t");

		printf("%6d,", x);
	}
	printf("\n};\n\n");
}

void main(void)
{
	int hl_value[] = HALFLIFE;
	int hl_count = sizeof(hl_value) / sizeof(int);
	int hl_idx, halflife;

	printf("/* SPDX-License-Identifier: GPL-2.0 */\n");
	printf("/* Generated by Documentation/scheduler/sched-pelt; do not modify. */\n");

	for (hl_idx = 0; hl_idx < hl_count; ++hl_idx) {
		halflife = hl_value[hl_idx];

		y = pow(0.5, 1/(double)halflife);
		sum = 1024;
		/* first period */
		max = 1024;
		n = -1;

		printf("\n#ifdef CONFIG_PELT_UTIL_HALFLIFE_%d\n", halflife);
		calc_runnable_avg_yN_inv(halflife);
		calc_runnable_avg_yN_sum(halflife);
		calc_converged_max(halflife);
		/*
		 * calc_accumulated_sum_32(halflife) precomputed load sum table of half-life,
		 * not used yet.
		 */
		printf("#endif\n");
	}
}