perf tools: Add utility function to detect SMT status

libperf-y += libstring.o

libperf-y += bitmap.o

libperf-y += hweight.o

libperf-y += smt.o

libperf-y += quote.o

libperf-y += strbuf.o

libperf-y += string.o

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <linux/bitops.h>

#include "api/fs/fs.h"

#include "smt.h"

int smt_on(void)

{

	static bool cached;

	static int cached_result;

	int cpu;

	int ncpu;

	if (cached)

		return cached_result;

	ncpu = sysconf(_SC_NPROCESSORS_CONF);

	for (cpu = 0; cpu < ncpu; cpu++) {

		unsigned long long siblings;

		char *str;

		size_t strlen;

		char fn[256];

		snprintf(fn, sizeof fn,

			"devices/system/cpu/cpu%d/topology/thread_siblings",

			cpu);

		if (sysfs__read_str(fn, &str, &strlen) < 0)

			continue;

		/* Entry is hex, but does not have 0x, so need custom parser */

		siblings = strtoull(str, NULL, 16);

		free(str);

		if (hweight64(siblings) > 1) {

			cached_result = 1;

			cached = true;

			break;

		}

	}

	if (!cached) {

		cached_result = 0;

		cached = true;

	}

	return cached_result;

}

#ifndef SMT_H

#define SMT_H 1

int smt_on(void);

#endif