Messages in this thread | | | Date | Thu, 21 Nov 2013 17:29:56 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 3/7] idle, thermal, acpi: Remove home grown idle implementations |
| |
On Thu, Nov 21, 2013 at 08:07:16AM -0800, Paul E. McKenney wrote: > On Thu, Nov 21, 2013 at 09:21:51AM +0100, Peter Zijlstra wrote: > > On Wed, Nov 20, 2013 at 04:54:06PM -0800, Jacob Pan wrote: > > > On Wed, 20 Nov 2013 17:04:53 +0100 > > > Peter Zijlstra <peterz@infradead.org> wrote: > > > > > > > People are starting to grow their own idle implementations in various > > > > disgusting ways. Collapse the lot and use the generic idle code to > > > > provide a proper idle cycle implementation. > > > > > > > +Paul > > > > > > RCU and others rely on is_idle_task() might be broken with the > > > consolidated idle code since caller of do_idle may have pid != 0. > > > > > > Should we use TS_POLL or introduce a new flag to identify idle task? > > > > PF_IDLE would be my preference, I checked and we seem to have a grand > > total of 2 unused task_struct::flags left ;-) > > As long as RCU has some reliable way to identify an idle task, I am > good. But I have to ask -- why can't idle injection coordinate with > the existing idle tasks rather than temporarily making alternative > idle tasks?
Because that'd completely wreck how the scheduler selects tasks for just these 2 arguably insane drivers.
We'd have to somehow teach it to pick the actual idle task instead of this one task, but keep scheduling the rest of the tasks like normal -- we very much should keep higher priority tasks running like normal.
And we'd need a way to make it stop doing this 'proxy' execution.
That said, once we manage to replace the entire PI implementation with a proper proxy execution scheme, the above would be possible by having a resource (rt_mutex) associated with every idle task, and always held by that task.
At that point we can do something like:
rt_mutex_lock_timeout(cpu_idle_lock(cpu), jiffies);
And get the idle thread executing in our stead.
That said, idle is _special_ and I'd not be surprised we'd find a few 'funnies' along the way of trying to get that to actually work.
For now I'd rather not go there quite yet.
| |