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Date: Thu, 21 Nov 2013 09:27:42 -0800 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Peter Zijlstra <peterz@...radead.org> Cc: Jacob Pan <jacob.jun.pan@...ux.intel.com>, Arjan van de Ven <arjan@...ux.intel.com>, lenb@...nel.org, rjw@...ysocki.net, Eliezer Tamir <eliezer.tamir@...ux.intel.com>, Chris Leech <christopher.leech@...el.com>, David Miller <davem@...emloft.net>, rui.zhang@...el.com, Mike Galbraith <bitbucket@...ine.de>, Ingo Molnar <mingo@...nel.org>, hpa@...or.com, Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com> Subject: Re: [PATCH 3/7] idle, thermal, acpi: Remove home grown idle implementations On Thu, Nov 21, 2013 at 05:29:56PM +0100, Peter Zijlstra wrote: > 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@...radead.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. Fair enough! Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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