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

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Date:   Wed, 21 Dec 2022 14:43:39 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        rafael@...nel.org
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] thermal/idle_inject: Support 100% idle injection


Hi Srinivas,


On 09/12/2022 02:36, Srinivas Pandruvada 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.

Good catch

> 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

Yes, from my POV a CPU being impossible to cool down for any reason 
should end up by staying off.

> 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.

Would it make sense to write a trace in this case ?

> 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().

Sounds good to me

> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> ---
>   drivers/powercap/idle_inject.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/powercap/idle_inject.c b/drivers/powercap/idle_inject.c
> index f48e71501429..4a4fe60d2563 100644
> --- a/drivers/powercap/idle_inject.c
> +++ b/drivers/powercap/idle_inject.c
> @@ -184,7 +184,7 @@ 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);
>   	}

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