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

From: Daniel Lezcano
Date: Wed Dec 21 2022 - 08:44:01 EST



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@xxxxxxxxxxxxxxx>
---
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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