Timer Tick Handling

mreff555 · 07-04-2013, 10:31 AM

Newer kernel version have more options about Tick Handling

Code:

Timer tick handling
  1. Periodic timer ticks (constant rate, no dynticks) (HZ_PERIODIC) (NEW)
> 2. Idle dynticks system (tickless idle) (NO_HZ_IDLE) (NEW)
  3. Full dynticks system (tickless) (NO_HZ_FULL) (NEW)
choice[1-3]:

I can infer a few things. I would guess that dynamic tics would be less accurate with the benefit of speed. Based on this I would think periodic would be the best choice for most desktop systems, but I would like some more insite in to this.

crosstalk · 07-05-2013, 02:35 PM

Dynamic ticks shuts off the normal periodic timer interrupt when a logical CPU is otherwise idle. This is no less accurate than periodic ticks -- however, it decreases power usage (often significantly) when the system is idle (and a periodic tick is unnecessary). This is actually a good idea on a desktop system.

Full dynamic ticks additionally shuts off the periodic interrupt when only one process is runnable on a given logical CPU. This may potentially improve performance for high-throughput tasks (perhaps latency-sensitive tasks as well?) if process affinities are set by hand. In essence, this lets someone who really cares about performance give a process full control of a logical CPU. This would also be an acceptable option for desktop systems.

In short, you probably won't notice a difference between NO_HZ_IDLE and NO_HZ_FULL, so choose whichever you want. I'd recommend against HZ_PERIODIC because it would increase power usage (it prevents a processor from going to sleep for any significant amount of time).