通过sysfs判断cpu是否支持smt

在kernel/cpu.c中为smt建立了一个sysfs的入口，代码如下：

可以看到支持smt的cpu 有一下五种状态
static const char *smt_states[] = {
	[CPU_SMT_ENABLED]		= "on",
	[CPU_SMT_DISABLED]		= "off",
	[CPU_SMT_FORCE_DISABLED]	= "forceoff",
	[CPU_SMT_NOT_SUPPORTED]		= "notsupported",
	[CPU_SMT_NOT_IMPLEMENTED]	= "notimplemented",
};

static ssize_t
show_smt_control(struct device *dev, struct device_attribute *attr, char *buf)
{
	const char *state = smt_states[cpu_smt_control];

	return snprintf(buf, PAGE_SIZE - 2, "%s\n", state);
}

static ssize_t
store_smt_control(struct device *dev, struct device_attribute *attr,
		  const char *buf, size_t count)
{
	return __store_smt_control(dev, attr, buf, count);
}
static DEVICE_ATTR(control, 0644, show_smt_control, store_smt_control);

static ssize_t
show_smt_active(struct device *dev, struct device_attribute *attr, char *buf)
{
	return snprintf(buf, PAGE_SIZE - 2, "%d\n", sched_smt_active());
}
static DEVICE_ATTR(active, 0444, show_smt_active, NULL);

static struct attribute *cpuhp_smt_attrs[] = {
	&dev_attr_control.attr,
	&dev_attr_active.attr,
	NULL
};

static const struct attribute_group cpuhp_smt_attr_group = {
	.attrs = cpuhp_smt_attrs,
	.name = "smt",
	NULL
};
找一款不支持smt的cpu ，实际cat 如下：

[root@ip134 /]# cd ./sys/devices/system/cpu/smt
[root@ip134 smt]# ls
active  control
[root@ip134 smt]# cat active
0
[root@ip134 smt]# cat control
notsupported