On 10 July 2013 13:11, Morten Rasmussen morten.rasmussen@arm.com wrote:
On Wed, Jul 10, 2013 at 03:10:15AM +0100, Arjan van de Ven wrote:
On 7/9/2013 8:55 AM, Morten Rasmussen wrote:
- mod_delayed_work_on(schedule_cpu(), system_wq, &dwork,
msecs_to_jiffies(INTERVAL));so thinking about this more, this really really should not be a work queue. a work queue will cause a large number of context switches for no reason (on Intel and AMD you can switch P state from interrupt context, and I'm pretty sure that holds for many ARM as well)
Agree. I should have made it clear this is only a temporary solution. I would prefer to tie the power scheduler to the existing scheduler tick instead so we don't wake up cpus unnecessarily. nohz may be able handle that for us. Also, currently the power scheduler updates all cpus. Going forward this would change to per cpu updates and partial updates of the global view to improve scalability.
For the packing tasks patches, we are using the periodic load balance sequence to update the activity like it is done for the cpu_power. I have planned to update the packing patches to see how it can cooperate with Morten patches as it has similar needs.
and in addition, it causes some really nasty cases, especially around real time tasks. Your workqueue will schedule a kernel thread, which will run BEHIND real time tasks, and such real time task will then never be able to start running at a higher performance.
(and with the delta between lowest and highest performance sometimes being 10x or more, the real time task will be running SLOW... quite possible longer than several milliseconds)
and all for no good reason; a normal timer running in irq context would be much better for this kind of thing!