On 10 July 2013 13:11, Morten Rasmussen <morten.rasmus...@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! >> >> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
