[RFC v2] cpuidle : Add support for pseudo-cpuidle driver

[Abhishek Goel]

This option adds support for a testing cpuidle driver, which allows
user to define custom idle states with their respective latencies and
residencies. This is useful for testing the behaviour of governors on
customized set of idle states.

This can be used as of now by hard-coding the customized set of cpuidle
states in the driver. Will add the capability of this driver to be used
as a module in subsequent patches.

Original idea and discussion for this patch can be found at:
https://lkml.org/lkml/2019/12/17/655

Signed-off-by: Abhishek Goel <huntbag@xxxxxxxxxxxxxxxxxx>
---

 v1-> v2 : Includes minor changes adapted from reviews.
           Also, there was a divergence from expected behaviour of idle
	   loop in v1. That has been fixed.

 drivers/cpuidle/Kconfig        |   9 ++
 drivers/cpuidle/Makefile       |   1 +
 drivers/cpuidle/cpuidle-test.c | 283 +++++++++++++++++++++++++++++++++
 3 files changed, 293 insertions(+)
 create mode 100644 drivers/cpuidle/cpuidle-test.c

diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig
index c0aeedd66f02..1a0f227d61d6 100644
--- a/drivers/cpuidle/Kconfig
+++ b/drivers/cpuidle/Kconfig
@@ -71,6 +71,15 @@ config HALTPOLL_CPUIDLE
 	 before halting in the guest (more efficient than polling in the
 	 host via halt_poll_ns for some scenarios).
 
+config TEST_CPUIDLE
+	tristate "cpuidle test driver"
+	default n
+	help
+	  This option enables a testing cpuidle driver, which allows the user
+	  to define custom idle states with their respective latencies & residencies.
+	  This is useful for testing the behaviour of governors on different
+	  sets of idle states.
+
 endif
 
 config ARCH_NEEDS_CPU_IDLE_COUPLED
diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile
index f07800cbb43f..68ea7dc257b5 100644
--- a/drivers/cpuidle/Makefile
+++ b/drivers/cpuidle/Makefile
@@ -8,6 +8,7 @@ obj-$(CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED) += coupled.o
 obj-$(CONFIG_DT_IDLE_STATES)		  += dt_idle_states.o
 obj-$(CONFIG_ARCH_HAS_CPU_RELAX)	  += poll_state.o
 obj-$(CONFIG_HALTPOLL_CPUIDLE)		  += cpuidle-haltpoll.o
+obj-$(CONFIG_TEST_CPUIDLE)		  += cpuidle-test.o
 
 ##################################################################################
 # ARM SoC drivers
diff --git a/drivers/cpuidle/cpuidle-test.c b/drivers/cpuidle/cpuidle-test.c
new file mode 100644
index 000000000000..45605f142dab
--- /dev/null
+++ b/drivers/cpuidle/cpuidle-test.c
@@ -0,0 +1,283 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  cpuidle-test - Test driver for cpuidle.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/moduleparam.h>
+#include <linux/cpuidle.h>
+#include <linux/cpu.h>
+#include <linux/module.h>
+#include <linux/sched/idle.h>
+#include <linux/sched/clock.h>
+#include <linux/sched/idle.h>
+
+#define CPUIDLE_STATE_MAX	10
+#define MAX_PARAM_LENGTH	100
+
+static unsigned int nr_states = 4;
+static unsigned int sim_type = 1;
+static char name[MAX_PARAM_LENGTH];
+static char latency_us[MAX_PARAM_LENGTH];
+static char residency_us[MAX_PARAM_LENGTH];
+
+
+module_param(nr_states, uint, 0644);
+module_param(sim_type, uint, 0644);
+module_param_string(name, name, MAX_PARAM_LENGTH, 0644);
+module_param_string(latency_us, latency_us, MAX_PARAM_LENGTH, 0644);
+module_param_string(residency_us, residency_us, MAX_PARAM_LENGTH, 0644);
+
+static struct cpuidle_driver test_cpuidle_driver = {
+	.name		= "test_cpuidle",
+	.owner		= THIS_MODULE,
+};
+
+static struct cpuidle_state *cpuidle_state_table __read_mostly;
+
+static struct cpuidle_device __percpu *test_cpuidle_devices;
+static enum cpuhp_state test_hp_idlestate;
+
+
+static int __cpuidle idle_loop(struct cpuidle_device *dev,
+				struct cpuidle_driver *drv,
+				int index)
+{
+	u64 time_start;
+
+	local_irq_enable();
+	if (!current_set_polling_and_test()) {
+		while (!need_resched())
+			cpu_relax();
+	}
+
+	time_start = local_clock();
+
+	/*
+	 * Currently, this while loop which is intended to introduce latency
+	 * for corresponding idle states, may not necessarily execute
+	 * completely if there is a interrupt in betweeen. This need to be
+	 * worked upon to distinguish among idle states.
+	 */
+	while (local_clock() - time_start < drv->states[index].exit_latency) {
+	}
+
+	current_clr_polling();
+
+	return index;
+}
+
+static struct cpuidle_state cpuidle_states[CPUIDLE_STATE_MAX] = {
+	{ /* Snooze */
+		.name = "snooze",
+		.exit_latency = 0,
+		.target_residency = 0,
+		.enter = idle_loop },
+};
+
+static struct cpuidle_state cpuidle_states_ppc[] = {
+	{	.name = "snooze",
+		.exit_latency = 0,
+		.target_residency = 0,
+		.enter = idle_loop },
+	{
+		.name = "stop0",
+		.exit_latency = 2,
+		.target_residency = 20,
+		.enter = idle_loop },
+	{
+		.name = "stop1",
+		.exit_latency = 5,
+		.target_residency = 50,
+		.enter = idle_loop },
+	{
+		.name = "stop2",
+		.exit_latency = 10,
+		.target_residency = 100,
+		.enter = idle_loop },
+};
+
+static struct cpuidle_state cpuidle_states_intel[] = {
+	{	.name = "poll",
+		.exit_latency = 0,
+		.target_residency = 0,
+		.enter = idle_loop },
+	{
+		.name = "c1",
+		.exit_latency = 2,
+		.target_residency = 2,
+		.enter = idle_loop },
+	{
+		.name = "c1e",
+		.exit_latency = 10,
+		.target_residency = 20,
+		.enter = idle_loop },
+	{
+		.name = "c3",
+		.exit_latency = 80,
+		.target_residency = 211,
+		.enter = idle_loop },
+};
+
+static int cpuidle_cpu_online(unsigned int cpu)
+{
+	struct cpuidle_device *dev;
+
+	dev = per_cpu_ptr(test_cpuidle_devices, cpu);
+	if (!dev->registered) {
+		dev->cpu = cpu;
+		if (cpuidle_register_device(dev)) {
+			pr_notice("cpuidle_register_device %d failed!\n", cpu);
+			return -EIO;
+		}
+	}
+
+	return 0;
+}
+
+static int cpuidle_cpu_dead(unsigned int cpu)
+{
+	struct cpuidle_device *dev;
+
+	dev = per_cpu_ptr(test_cpuidle_devices, cpu);
+	if (dev->registered)
+		cpuidle_unregister_device(dev);
+
+	return 0;
+}
+
+static int cpuidle_driver_init(void)
+{
+	int idle_state;
+	struct cpuidle_driver *drv = &test_cpuidle_driver;
+
+	drv->state_count = 0;
+
+	for (idle_state = 0; idle_state < nr_states; ++idle_state) {
+		/* Is the state not enabled? */
+		if (cpuidle_state_table[idle_state].enter == NULL)
+			continue;
+
+		drv->states[drv->state_count] =	/* structure copy */
+			cpuidle_state_table[idle_state];
+
+		drv->state_count += 1;
+	}
+
+	return 0;
+}
+
+static int add_cpuidle_states(void)
+{
+	/* Parse the module param and initialize the idle states here
+	 * in cpuidle_state_table.
+	 */
+	char *this_param;
+	char *input_name = name;
+	char *input_res = residency_us;
+	char *input_lat = latency_us;
+	int index = 1;
+	long temp;
+	int rc;
+
+	switch (sim_type) {
+	case 1:
+		cpuidle_state_table = cpuidle_states_ppc;
+		return 0;
+	case 2:
+		cpuidle_state_table = cpuidle_states_intel;
+		return 0;
+	case 3:
+		break;
+	default:
+		pr_warn("Sim value out of bound\n");
+		break;
+	}
+
+	if (strnlen(input_name, MAX_PARAM_LENGTH)) {
+		while ((this_param = strsep(&input_name, ",")) && index <= nr_states) {
+			strcpy(cpuidle_states[index].name, this_param);
+			cpuidle_states[index].enter = idle_loop;
+			index++;
+		}
+	}
+
+	if (strnlen(input_res, MAX_PARAM_LENGTH)) {
+		index = 1;
+		while ((this_param = strsep(&input_res, ",")) && index <= nr_states) {
+			rc = kstrtol(this_param, 10, &temp);
+			cpuidle_states[index].target_residency = temp;
+			index++;
+		}
+	}
+
+	if (strnlen(input_lat, MAX_PARAM_LENGTH)) {
+		index = 1;
+		while ((this_param = strsep(&input_lat, ",")) && index <= nr_states) {
+			rc = kstrtol(this_param, 10, &temp);
+			cpuidle_states[index].exit_latency = temp;
+			index++;
+		}
+	}
+
+	cpuidle_state_table = cpuidle_states;
+	return nr_states;
+}
+
+static void test_cpuidle_uninit(void)
+{
+	if (test_hp_idlestate)
+		cpuhp_remove_state(test_hp_idlestate);
+	cpuidle_unregister_driver(&test_cpuidle_driver);
+
+	free_percpu(test_cpuidle_devices);
+	test_cpuidle_devices = NULL;
+}
+
+static int __init test_cpuidle_init(void)
+{
+	int retval;
+
+	add_cpuidle_states();
+	cpuidle_driver_init();
+	retval = cpuidle_register(&test_cpuidle_driver, NULL);
+	if (retval) {
+		printk(KERN_DEBUG "Registration of test driver failed.\n");
+		return retval;
+	}
+
+	test_cpuidle_devices = alloc_percpu(struct cpuidle_device);
+	if (test_cpuidle_devices == NULL) {
+		cpuidle_unregister_driver(&test_cpuidle_driver);
+		return -ENOMEM;
+	}
+
+	retval = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+					   "cpuidle/powernv:online",
+					   cpuidle_cpu_online,
+					   cpuidle_cpu_dead);
+
+	if (retval < 0) {
+		test_cpuidle_uninit();
+	} else {
+		test_hp_idlestate = retval;
+		retval = 0;
+	}
+
+	return retval;
+}
+
+static void __exit test_cpuidle_exit(void)
+{
+	test_cpuidle_uninit();
+}
+
+module_init(test_cpuidle_init);
+module_exit(test_cpuidle_exit);
+MODULE_DESCRIPTION("Test Cpuidle Driver");
+MODULE_AUTHOR("Abhishek Goel");
+MODULE_LICENSE("GPL");
+
-- 
2.17.1