On 20 February 2015 at 18:52, Ingo Molnar mingo@kernel.org wrote:
- Viresh Kumar viresh.kumar@linaro.org wrote:
CLOCK_EVT_DEV_MODE_UNUSED = 0,What is 'unused' - not initialized yet?
Unused. Initially all clockevent devices are supposed to be in this mode but later if another device replaces an existing one, the existing one is put into this mode.
CLOCK_EVT_DEV_MODE_SHUTDOWN,CLOCK_EVT_DEV_MODE_PERIODIC,CLOCK_EVT_DEV_MODE_ONESHOT,CLOCK_EVT_DEV_MODE_RESUME,What is 'resume' mode?
Introduced with: 18de5bc4c1f1 ("clockevents: fix resume logic") and is only called during system resume to resume the clockevent devices before resuming the tick. Only few implementations do meaningful stuff here.
CLOCK_EVT_DEV_MODE_ONESHOT_STOPPED, /* This would be the newmode which I will add later */
What does this mode express?
I have added it here to show how things would look like eventually, but it wouldn't be present in the patch which splits the enum into two parts..
Its only important for NOHZ_FULL (IDLE ? Maybe). When we decide that the tick (LOWRES) or hrtimer interrupt (HIGHRES) isn't required for indefinite period of time (i.e. no timers/hrtimers are present to serve), we skip reprogramming the clockevent device. But its already reprogrammed from the tick-handler and so will fire atleast once again.
The case is worst for implementations where the underlying hardware doesn't have support for ONESHOT mode. And so they emulate ONESHOT over PERIODIC. And in those cases, these spurious interrupts come at a rate last programmed for the clockevent device. And that is mostly tick-rate..
So for state machines it's important to document the states and the transitions between them very clearly - please start with that.
Sure.
Also, this should not be in a generic header, it should be somewhere internal in kernel/time/.
Right. But there are some excellent drivers which are comparing things against dev->mode (i.e. enum clock_event_dev_mode now..). I need to fix them as well first to push this into some internal header.
Ofcourse, we also need to replace 'clock_event_mode' with 'clock_event_dev_mode' and 'CLOCK_EVT_MODE_*' with 'CLOCK_EVT_DEV_MODE_*' in all core code..
Yes.
Thanks for your suggestions.