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

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Message-ID: <CAJZ5v0iLf5JpdzRnjk+TxKVuX2GkLx4-0p8SJb1uxFsKGe0ksg@mail.gmail.com>
Date:   Mon, 28 Nov 2016 22:39:07 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Petr Mladek <pmladek@...e.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: 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@...ux.intel.com> wrote:
> From: Peter Zijlstra <peterz@...radead.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@...nel.org>
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>

Have you made any changes to the original Peter's patch, or is this
just a resend of that?

Thanks,
Rafael