// SPDX-License-Identifier: GPL-2.0
/*
 * Preempt / IRQ disable delay thread to test latency tracers
 *
 * Copyright (C) 2018 Joel Fernandes (Google) <joel@joelfernandes.org>
 */

#include <linux/trace_clock.h>
#include <linux/delay.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/kernel.h>
#include <linux/kobject.h>
#include <linux/kthread.h>
#include <linux/module.h>
#include <linux/printk.h>
#include <linux/string.h>
#include <linux/sysfs.h>
#include <linux/completion.h>

static ulong delay = 100;
static char test_mode[12] = "irq";
static uint burst_size = 1;
static int  cpu_affinity = -1;

module_param_named(delay, delay, ulong, 0444);
module_param_string(test_mode, test_mode, 12, 0444);
module_param_named(burst_size, burst_size, uint, 0444);
module_param_named(cpu_affinity, cpu_affinity, int, 0444);
MODULE_PARM_DESC(delay, "Period in microseconds (100 us default)");
MODULE_PARM_DESC(test_mode, "Mode of the test such as preempt, irq, or alternate (default irq)");
MODULE_PARM_DESC(burst_size, "The size of a burst (default 1)");
MODULE_PARM_DESC(cpu_affinity, "Cpu num test is running on");

static struct completion done;

static void busy_wait(ulong time)
{
        u64 start, end;

        start = trace_clock_local();

        do {
                end = trace_clock_local();
                if (kthread_should_stop())
                        break;
        } while ((end - start) < (time * 1000));
}

static __always_inline void irqoff_test(void)
{
        unsigned long flags;

        local_irq_save(flags);
        busy_wait(delay);
        local_irq_restore(flags);
}

static __always_inline void preemptoff_test(void)
{
        preempt_disable();
        busy_wait(delay);
        preempt_enable();
}

static void execute_preemptirqtest(int idx)
{
        if (!strcmp(test_mode, "irq"))
                irqoff_test();
        else if (!strcmp(test_mode, "preempt"))
                preemptoff_test();
        else if (!strcmp(test_mode, "alternate")) {
                if (idx % 2 == 0)
                        irqoff_test();
                else
                        preemptoff_test();
        }
}

#define DECLARE_TESTFN(POSTFIX)                         \
        static void preemptirqtest_##POSTFIX(int idx)   \
        {                                               \
                execute_preemptirqtest(idx);            \
        }                                               \

/*
 * We create 10 different functions, so that we can get 10 different
 * backtraces.
 */
DECLARE_TESTFN(0)
DECLARE_TESTFN(1)
DECLARE_TESTFN(2)
DECLARE_TESTFN(3)
DECLARE_TESTFN(4)
DECLARE_TESTFN(5)
DECLARE_TESTFN(6)
DECLARE_TESTFN(7)
DECLARE_TESTFN(8)
DECLARE_TESTFN(9)

static void (*testfuncs[])(int)  = {
        preemptirqtest_0,
        preemptirqtest_1,
        preemptirqtest_2,
        preemptirqtest_3,
        preemptirqtest_4,
        preemptirqtest_5,
        preemptirqtest_6,
        preemptirqtest_7,
        preemptirqtest_8,
        preemptirqtest_9,
};

#define NR_TEST_FUNCS ARRAY_SIZE(testfuncs)

static int preemptirq_delay_run(void *data)
{
        int i;
        int s = MIN(burst_size, NR_TEST_FUNCS);
        cpumask_var_t cpu_mask;

        if (!alloc_cpumask_var(&cpu_mask, GFP_KERNEL))
                return -ENOMEM;

        if (cpu_affinity > -1) {
                cpumask_clear(cpu_mask);
                cpumask_set_cpu(cpu_affinity, cpu_mask);
                if (set_cpus_allowed_ptr(current, cpu_mask))
                        pr_err("cpu_affinity:%d, failed\n", cpu_affinity);
        }

        for (i = 0; i < s; i++)
                (testfuncs[i])(i);

        complete(&done);

        set_current_state(TASK_INTERRUPTIBLE);
        while (!kthread_should_stop()) {
                schedule();
                set_current_state(TASK_INTERRUPTIBLE);
        }

        __set_current_state(TASK_RUNNING);

        free_cpumask_var(cpu_mask);

        return 0;
}

static int preemptirq_run_test(void)
{
        struct task_struct *task;
        char task_name[50];

        init_completion(&done);

        snprintf(task_name, sizeof(task_name), "%s_test", test_mode);
        task =  kthread_run(preemptirq_delay_run, NULL, task_name);
        if (IS_ERR(task))
                return PTR_ERR(task);
        if (task) {
                wait_for_completion(&done);
                kthread_stop(task);
        }
        return 0;
}


static ssize_t trigger_store(struct kobject *kobj, struct kobj_attribute *attr,
                         const char *buf, size_t count)
{
        ssize_t ret;

        ret = preemptirq_run_test();
        if (ret)
                return ret;
        return count;
}

static struct kobj_attribute trigger_attribute =
        __ATTR(trigger, 0200, NULL, trigger_store);

static struct attribute *attrs[] = {
        &trigger_attribute.attr,
        NULL,
};

static struct attribute_group attr_group = {
        .attrs = attrs,
};

static struct kobject *preemptirq_delay_kobj;

static int __init preemptirq_delay_init(void)
{
        int retval;

        retval = preemptirq_run_test();
        if (retval != 0)
                return retval;

        preemptirq_delay_kobj = kobject_create_and_add("preemptirq_delay_test",
                                                       kernel_kobj);
        if (!preemptirq_delay_kobj)
                return -ENOMEM;

        retval = sysfs_create_group(preemptirq_delay_kobj, &attr_group);
        if (retval)
                kobject_put(preemptirq_delay_kobj);

        return retval;
}

static void __exit preemptirq_delay_exit(void)
{
        kobject_put(preemptirq_delay_kobj);
}

module_init(preemptirq_delay_init)
module_exit(preemptirq_delay_exit)
MODULE_DESCRIPTION("Preempt / IRQ disable delay thread to test latency tracers");
MODULE_LICENSE("GPL v2");