Re: [PATCH 01/10] tick/nohz: Prevent tick_nohz_get_sleep_length() from returning negative value

[Peter Zijlstra]

On Thu, Mar 11, 2021 at 01:36:59PM +0100, Frederic Weisbecker wrote:
> From: "Zhou Ti (x2019cwm)" <x2019cwm@xxxxxxx>
> 
> If the hardware clock happens to fire its interrupts late, two possible
> issues can happen while calling tick_nohz_get_sleep_length(). Either:
> 
> 1) The next clockevent device event is due past the last idle entry time.
> 
> or:
> 
> 2) The last timekeeping update happened before the last idle entry time
>    and the next timer callback expires before the last idle entry time.
> 
> Make sure that both cases are handled to avoid returning a negative
> duration to the cpuidle governors.

Why? ... and wouldn't it be cheaper the fix the caller to
check negative once, instead of adding two branches here?