linux-kernel - Re: [PATCH] thermal/idle_inject: Support 100% idle injection

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Message-ID: <CAJZ5v0gnx4R0M86O5+Eth4kEoxk1-=Ym7Wrs0-DzRUsvAvR-KA@mail.gmail.com>
Date:   Fri, 20 Jan 2023 18:30:15 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     rafael@...nel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, daniel.lezcano@...aro.org,
        rui.zhang@...el.com
Subject: Re: [PATCH] thermal/idle_inject: Support 100% idle injection

It's powercap/idle_inject.

On Tue, Jan 17, 2023 at 7:23 PM Srinivas Pandruvada
<srinivas.pandruvada@...ux.intel.com> wrote:
>
> The users of idle injection framework allow 100% idle injection. For
> example: thermal/cpuidle_cooling.c driver. When the ratio set to 100%,
> the runtime_duration becomes zero.
>
> In the function idle_inject_set_duration() in idle injection framework
> run_duration_us == 0 is silently ignored, without any error (it is a
> void function). So, the caller will assume that everything is fine and
> 100% idle is effective. But in reality the idle inject will be whatever
> set before.
>
> There are two options:
> - The caller change their max state to 99% instead of 100% and
> document that 100% is not supported by idle inject framework
> - Support 100% idle support in idle inject framework
>
> Since there are other protections via RT throttling, this framework can
> allow 100% idle. The RT throttling will be activated at 95% idle by
> default. The caller disabling RT throttling and injecting 100% idle,
> should be aware that CPU can't be used at all.
>
> The idle inject timer is started for (run_duration_us + idle_duration_us)
> duration. Hence replace (run_duration_us && idle_duration_us) with
> (run_duration_us + idle_duration_us) in the function
> idle_inject_set_duration(). Also check for !(run_duration_us +
> idle_duration_us) to return -EINVAL in the function idle_inject_start().

And I have edited the changelog somewhat.

> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> ---
> Change log:
> Compared to RFC/RFT
> - Add a pr_debug for 100% idle
>
>  drivers/powercap/idle_inject.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/powercap/idle_inject.c b/drivers/powercap/idle_inject.c
> index c57b40477246..3ac81086d71f 100644
> --- a/drivers/powercap/idle_inject.c
> +++ b/drivers/powercap/idle_inject.c
> @@ -170,10 +170,12 @@ void idle_inject_set_duration(struct idle_inject_device *ii_dev,
>                               unsigned int run_duration_us,
>                               unsigned int idle_duration_us)
>  {
> -       if (run_duration_us && idle_duration_us) {
> +       if (run_duration_us + idle_duration_us) {
>                 WRITE_ONCE(ii_dev->run_duration_us, run_duration_us);
>                 WRITE_ONCE(ii_dev->idle_duration_us, idle_duration_us);
>         }
> +       if (!run_duration_us)
> +               pr_debug("CPU is forced to 100 percent idle\n");
>  }
>  EXPORT_SYMBOL_NS_GPL(idle_inject_set_duration, IDLE_INJECT);
>
> @@ -219,7 +221,7 @@ int idle_inject_start(struct idle_inject_device *ii_dev)
>         unsigned int idle_duration_us = READ_ONCE(ii_dev->idle_duration_us);
>         unsigned int run_duration_us = READ_ONCE(ii_dev->run_duration_us);
>
> -       if (!idle_duration_us || !run_duration_us)
> +       if (!(idle_duration_us + run_duration_us))
>                 return -EINVAL;
>
>         pr_debug("Starting injecting idle cycles on CPUs '%*pbl'\n",
> --

Applied as 6.3 material, thanks!