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

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  Re: [PATCH v4 1/2] idle: add support for tasks that inject idle "Rafael J. Wysocki" <rafael@kernel.org> - 2016-11-28 22:40 +0100
    Re: [PATCH v4 1/2] idle: add support for tasks that inject idle Jacob Pan <jacob.jun.pan@linux.intel.com> - 2016-11-28 22:50 +0100
      Re: [PATCH v4 1/2] idle: add support for tasks that inject idle "Rafael J. Wysocki" <rafael@kernel.org> - 2016-11-28 23:30 +0100

#1531687 — Re: [PATCH v4 1/2] idle: add support for tasks that inject idle

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?

Thanks,
Rafael

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#1531715

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.

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#1531742

On Mon, Nov 28, 2016 at 10:46 PM, Jacob Pan
<jacob.jun.pan@linux.intel.com> wrote:
> 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.

OK, thanks!

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