内核定时机制API之__round_jiffies

unsigned long __round_jiffies(unsigned long j, int cpu)用户将jiffies 转成HZ的整数倍也就是整秒.
其源码分析如下：
unsigned long __round_jiffies(unsigned long j, int cpu)
{
return round_jiffies_common(j, cpu, false);
}
static unsigned long round_jiffies_common(unsigned long j, int cpu,
bool force_up)
{
int rem;
unsigned long original = j;

j += cpu * 3;

rem = j % HZ;

#这里的force_up等于false，所以这里分解rem < HZ/4 来决定是round_down还是round_up
if (rem < HZ/4 && !force_up) /* round down */
j = j - rem;
else /* round up */
j = j - rem + HZ;

/* now that we have rounded, subtract the extra skew again */
j -= cpu * 3;

/*
* Make sure j is still in the future. Otherwise return the
* unmodified value.
*/
#看当前的jiffies是否已经比形参j快了，一般情况下应该不会，所以这里返回round后的j
return time_is_after_jiffies(j) ? j : original;
}
从这里看到cpu 个数越大，这个函数返回的值越大.