Re: [RFC] sched: Ensure cpu_power periodic update

On Mon, 2011-12-12 at 20:21 +0100, Vincent Guittot wrote:

With a lot of small tasks, the softirq sched is nearly never called when no_hz is enable. In this case the load_balance is mainly called with the newly_idle mode which doesn't update the cpu_power. Add a next_update field which ensure a maximum update period when there is short activity

• if (local_group) {

• if (idle != CPU_NEWLY_IDLE) {
  

• 	if (balance_cpu != this_cpu) {
  

• 		*balance = 0;
  

• 		return;
  

• 	}
  

• 	update_group_power(sd, this_cpu);
  

• } else if (time_after_eq(jiffies, group->sgp->next_update))
  

• 	update_group_power(sd, this_cpu);
  

  }

Hmm, I would have expected it to be called from the NOHZ balancing path instead of the new_idle path. Your changelog fails to mentions any considerations on this..

Then again, its probably easier to keep update_group_power on this_cpu than to allow a remote update of your cpu_power.

So I'm not opposed to this patch, I'd just like a little extra clarification.