// 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);} static void __exit preemptirq_delay_exit(void){	return;} module_init(preemptirq_delay_init)module_exit(preemptirq_delay_exit)MODULE_LICENSE("GPL v2");