linux-kernel - [PATCH 06/23] sched,psci: Convert to sched_set

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Date:   Wed, 22 Apr 2020 13:27:25 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org, linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, rostedt@...dmis.org, qais.yousef@....com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, bsegall@...gle.com, mgorman@...e.de,
        peterz@...radead.org, daniel.lezcano@...aro.org,
        sudeep.holla@....com
Subject: [PATCH 06/23] sched,psci: Convert to sched_set_fifo*()

Because SCHED_FIFO is a broken scheduler model (see previous patches)
take away the priority field, the kernel can't possibly make an
informed decision.

Effectively changes prio from 99 to 50.

XXX this thing is horrific, it basically open-codes a stop-machine and
idle.

Cc: daniel.lezcano@...aro.org
Cc: sudeep.holla@....com
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Ingo Molnar <mingo@...nel.org>
---
 drivers/firmware/psci/psci_checker.c |   11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

--- a/drivers/firmware/psci/psci_checker.c
+++ b/drivers/firmware/psci/psci_checker.c
@@ -272,7 +272,6 @@ static int suspend_test_thread(void *arg
 {
 	int cpu = (long)arg;
 	int i, nb_suspend = 0, nb_shallow_sleep = 0, nb_err = 0;
-	struct sched_param sched_priority = { .sched_priority = MAX_RT_PRIO-1 };
 	struct cpuidle_device *dev;
 	struct cpuidle_driver *drv;
 	/* No need for an actual callback, we just want to wake up the CPU. */
@@ -282,9 +281,8 @@ static int suspend_test_thread(void *arg
 	wait_for_completion(&suspend_threads_started);
 
 	/* Set maximum priority to preempt all other threads on this CPU. */
-	if (sched_setscheduler_nocheck(current, SCHED_FIFO, &sched_priority))
-		pr_warn("Failed to set suspend thread scheduler on CPU %d\n",
-			cpu);
+	if (sched_set_fifo(current))
+		pr_warn("Failed to set suspend thread scheduler on CPU %d\n", cpu);
 
 	dev = this_cpu_read(cpuidle_devices);
 	drv = cpuidle_get_cpu_driver(dev);
@@ -349,11 +347,6 @@ static int suspend_test_thread(void *arg
 	if (atomic_dec_return_relaxed(&nb_active_threads) == 0)
 		complete(&suspend_threads_done);
 
-	/* Give up on RT scheduling and wait for termination. */
-	sched_priority.sched_priority = 0;
-	if (sched_setscheduler_nocheck(current, SCHED_NORMAL, &sched_priority))
-		pr_warn("Failed to set suspend thread scheduler on CPU %d\n",
-			cpu);
 	for (;;) {
 		/* Needs to be set first to avoid missing a wakeup. */
 		set_current_state(TASK_INTERRUPTIBLE);