Re: [PATCH v4 1/2] idle: add support for tasks that inject idle

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

On Mon, 28 Nov 2016 22:39:07 +0100
"Rafael J. Wysocki" <rafael@kernel.org> wrote:

> On Mon, Nov 28, 2016 at 10:33 PM, Jacob Pan
> <jacob.jun.pan@linux.intel.com> wrote:
> > From: Peter Zijlstra <peterz@infradead.org>
> >
> > Idle injection drivers such as Intel powerclamp and ACPI PAD
> > drivers use realtime tasks to take control of CPU then inject idle.
> > There are two issues with this approach:
> >
> >  1. Low efficiency: injected idle task is treated as busy so sched
> > ticks do not stop during injected idle period, the result of these
> >     unwanted wakeups can be ~20% loss in power savings.
> >
> >  2. Idle accounting: injected idle time is presented to user as
> > busy.
> >
> > This patch addresses the issues by introducing a new PF_IDLE flag
> > which allows any given task to be treated as idle task while the
> > flag is set. Therefore, idle injection tasks can run through the
> > normal flow of NOHZ idle enter/exit to get the correct accounting
> > as well as tick stop when possible.
> >
> > The implication is that idle task is then no longer limited to PID
> > == 0.
> >
> > Acked-by: Ingo Molnar <mingo@kernel.org>
> > Signed-off-by: Peter Zijlstra <peterz@infradead.org>
> > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> 
> Have you made any changes to the original Peter's patch, or is this
> just a resend of that?
No changes made to Peter's patch. I just rebased to v4.9-rc7 and tested
it.