linux-imx

// 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/kthread.h>

#include <linux/module.h>

#include <linux/printk.h>

#include <linux/string.h>

​

static ulong delay = 100;

static char test_mode[10] = "irq";

​

module_param_named(delay, delay, ulong, S_IRUGO);

module_param_string(test_mode, test_mode, 10, S_IRUGO);

MODULE_PARM_DESC(delay, "Period in microseconds (100 uS default)");

MODULE_PARM_DESC(test_mode, "Mode of the test such as preempt or irq (default irq)");

​

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 int preemptirq_delay_run(void *data)

{

    unsigned long flags;

​

    if (!strcmp(test_mode, "irq")) {

        local_irq_save(flags);

        busy_wait(delay);

        local_irq_restore(flags);

    } else if (!strcmp(test_mode, "preempt")) {

        preempt_disable();

        busy_wait(delay);

        preempt_enable();

    }

​

    return 0;

}

​

static int __init preemptirq_delay_init(void)

{

    char task_name[50];

    struct task_struct *test_task;

​

    snprintf(task_name, sizeof(task_name), "%s_test", test_mode);

​

    test_task = kthread_run(preemptirq_delay_run, NULL, task_name);

    return PTR_ERR_OR_ZERO(test_task);

}