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

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Message-Id: <20221209013640.943210-1-srinivas.pandruvada@linux.intel.com>
Date:   Thu,  8 Dec 2022 17:36:40 -0800
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     rafael@...nel.org, daniel.lezcano@...aro.org
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: [RFC][PATCH] thermal/idle_inject: Support 100% idle injection

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().

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);
 	}
-- 
2.37.2