On Tue, 31 Jul 2018, Xu YiPing wrote:
> On 2018/7/30 19:03, Thomas Gleixner wrote:
> >
> > __internal_add_timer(base, timer)
> > {
> > idx = calc_wheel_index(1, 1)
> > {
> > delta = 1 - 1; <- 0
> >
> > if (0 < LVL_START(1))
> > idx = calc_index(1, 0)
> > {
> > expires = (1 + LVL_GRAN(0) - 1) >> LVL_SHIFT(0);
> > ----> expires = 0
>
> LVL_GRAN(0) = 1 and LVL_SHIFT(0) = 0
>
> after the calculation, expires = 1 ?
Indeed. You're right. Math is hard... So the index would be 1 and still not
fulfil the below:
> > mod_timer(timer, jiffies + 1)
> >
> > will not fire before aty least one jiffy has elapsed. Let's look at the
> > time line:
> >
> > |-------------------|-------------------|----------------|
> > tick tick tick
> > jiffies jiffies + 1 jiffies + 2
> >
> > | |
> > | Any timer armed | ^
> > | here must be | |
> > | queued here -------------------------|
> >
> > in order to guarantee that. Timer wheel timers are not accurate and never
> > can be.
Thanks,
tglx
