On 9/27/19 2:41 PM, Marc Zyngier wrote: > On 2019-09-27 13:36, Benjamin GAIGNARD wrote: >> On 9/27/19 1:22 PM, Marc Zyngier wrote: >>> On 2019-09-27 09:48, Benjamin Gaignard wrote: >>>> Adding always-on makes arm arch_timer claim to be an high resolution >>>> timer. >>>> That is possible because power mode won't stop clocking the timer. >>> >>> The "always-on" is not about the clock. It is about the comparator. >>> The clock itself is *guaranteed* to always tick. If it didn't, >>> that'd be >>> an integration bug, and a pretty bad one. >>> >>> What you're claiming here is that your CPU never enters a low-power >>> mode? >>> Ever? I find this very hard to believe. >>> >>> Furthermore, claiming that always-on is the way to force the arch-timer >>> to be an hrtimer is factually wrong. This is what happens *if* this is >>> the only timer in the system. The only case this is true is for virtual >>> machines. Anything else has a global timer somewhere that will allow >>> the arch timers to be used as an hrtimer. >>> >>> I'm pretty sure you too have a global timer somewhere in your system. >>> Enable it, and enjoy hrtimers without having to lie about the >>> properties >>> of your system! ;-) >> >> Hi Marc, >> >> This SoC doesn't have any other global timer. Use arch_time is the only >> we have to provide hrtimer on this system. > > And you don't have any form of power management either? What happens when > your CPU goes into idle? If your system does any form of power management > *and* doesn't have a separate timer, it is remarkably broken. Even in low-power modes this timer is always powered and clocked so it is working fine. > > M.
