On 20-05-15, 15:09, Thomas Gleixner wrote:
On Wed, 20 May 2015, Viresh Kumar wrote:
They look at clock_event_mode and not at state, right?
Yeah, it was all useful (that's what I thought initially, but not anymore) only when we migrate some drivers to the new per-state APIs.
And that way we add the overhead of a full function call to those drivers for the interrupt hot path?
Honestly, I didn't realize that this can be a blocker. My bad.
Of course you should have done that analysis before posting some random helper functions.
I did looked at all the drivers few days back, but failed to give a summary similar to yours. No excuses.
Lets look how useful these functions are for the various use cases
#1) Adds function call over head to the timer interrupt
Hot path does matter and that function call is a regression. So that's a NONO
Now explain me how your magic functions help. For most of the cases they would be a performance regression. And for the rest they really do not matter at all.
They wouldn't help at all in that case.
So, probably we are left with following choices:
- Maintain state internally within the driver. SMP cases need per-cpu storage as clkevt devices are per-cpu. Probably that's a NONO as well ?
- Use CLK_EVT_STATE_* directly in drivers (similar to the way we use CLK_EVT_MODE_* today).
- Write the routines I proposed as macros or inline functions in clockchips.h, and use them. Of course that wouldn't stop exposing CLK_EVT_STATE_* to rest of the kernel.
- Something else ?
Which one do you suggest ?