Commit f96e8577 authored by Joel Fernandes (Google)'s avatar Joel Fernandes (Google) Committed by Steven Rostedt (VMware)
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lib: Add module for testing preemptoff/irqsoff latency tracers 

Here we introduce a test module for introducing a long preempt or irq
disable delay in the kernel which the preemptoff or irqsoff tracers can
detect. This module is to be used only for test purposes and is default
disabled.

Following is the expected output (only briefly shown) that can be parsed
to verify that the tracers are working correctly. We will use this from
the kselftests in future patches.

For the preemptoff tracer:

echo preemptoff > /d/tracing/current_tracer
sleep 1
insmod ./preemptirq_delay_test.ko test_mode=preempt delay=500000
sleep 1
bash-4.3# cat /d/tracing/trace
preempt -1066    2...2    0us@: preemptirq_delay_run <-preemptirq_delay_run
preempt -1066    2...2 500002us : preemptirq_delay_run <-preemptirq_delay_run
preempt -1066    2...2 500004us : tracer_preempt_on <-preemptirq_delay_run
preempt -1066    2...2 500012us : <stack trace>
 => kthread
 => ret_from_fork

For the irqsoff tracer:

echo irqsoff > /d/tracing/current_tracer
sleep 1
insmod ./preemptirq_delay_test.ko test_mode=irq delay=500000
sleep 1
bash-4.3# cat /d/tracing/trace
irq dis -1069    1d..1    0us@: preemptirq_delay_run
irq dis -1069    1d..1 500001us : preemptirq_delay_run
irq dis -1069    1d..1 500002us : tracer_hardirqs_on <-preemptirq_delay_run
irq dis -1069    1d..1 500005us : <stack trace>
 => ret_from_fork

Link: http://lkml.kernel.org/r/20180712213611.GA8743@joelaf.mtv.corp.google.com



Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Julia Cartwright <julia@ni.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Thomas Glexiner <tglx@linutronix.de>
Cc: Todd Kjos <tkjos@google.com>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
[ Erick is a co-developer of this commit ]
Signed-off-by: default avatarErick Reyes <erickreyes@google.com>
Signed-off-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 2b27ece6

kernel/trace/Kconfig

+15 −0
Original line number Diff line number Diff line
@@ -687,6 +687,21 @@ config RING_BUFFER_STARTUP_TEST 


	 If unsure, say N



config PREEMPTIRQ_DELAY_TEST

	tristate "Preempt / IRQ disable delay thread to test latency tracers"

	depends on m

	help

	  Select this option to build a test module that can help test latency

	  tracers by executing a preempt or irq disable section with a user

	  configurable delay. The module busy waits for the duration of the

	  critical section.



	  For example, the following invocation forces a one-time irq-disabled

	  critical section for 500us:

	  modprobe preemptirq_delay_test test_mode=irq delay=500000



	  If unsure, say N



config TRACE_EVAL_MAP_FILE

       bool "Show eval mappings for trace events"

       depends on TRACING

kernel/trace/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ obj-$(CONFIG_TRACING) += trace_seq.o 
obj-$(CONFIG_TRACING) += trace_stat.o

obj-$(CONFIG_TRACING) += trace_printk.o

obj-$(CONFIG_TRACING_MAP) += tracing_map.o

obj-$(CONFIG_PREEMPTIRQ_DELAY_TEST) += preemptirq_delay_test.o

obj-$(CONFIG_CONTEXT_SWITCH_TRACER) += trace_sched_switch.o

obj-$(CONFIG_FUNCTION_TRACER) += trace_functions.o

obj-$(CONFIG_PREEMPTIRQ_EVENTS) += trace_irqsoff.o

kernel/trace/preemptirq_delay_test.c

0 → 100644
+72 −0
Original line number Diff line number Diff line 
// 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/delay.h>

#include <linux/interrupt.h>

#include <linux/irq.h>

#include <linux/kernel.h>

#include <linux/kthread.h>

#include <linux/ktime.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)

{

	ktime_t start, end;

	start = ktime_get();

	do {

		end = ktime_get();

		if (kthread_should_stop())

			break;

	} while (ktime_to_ns(ktime_sub(end, start)) < (time * 1000));

}



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");

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