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Subject[PATCH 2/4] preemptirq_delay_test: Add the burst feature and a sysfs trigger
Date
This burst feature enables the user to generate a burst of
preempt/irqsoff latencies. This makes it possible to test whether we
are able to detect latencies that systematically occur very close to
each other.

In addition, there is a sysfs trigger, so that it's not necessary to
reload the module to repeat the test. The trigger will appear as
/sys/kernel/preemptirq_delay_test/trigger in sysfs.

Signed-off-by: Viktor Rosendahl <Viktor.Rosendahl@bmw.de>
---
kernel/trace/preemptirq_delay_test.c | 139 +++++++++++++++++++++++----
1 file changed, 120 insertions(+), 19 deletions(-)

diff --git a/kernel/trace/preemptirq_delay_test.c b/kernel/trace/preemptirq_delay_test.c
index d8765c952fab..1fc3cdbdd293 100644
--- a/kernel/trace/preemptirq_delay_test.c
+++ b/kernel/trace/preemptirq_delay_test.c
@@ -3,6 +3,7 @@
* Preempt / IRQ disable delay thread to test latency tracers
*
* Copyright (C) 2018 Joel Fernandes (Google) <joel@joelfernandes.org>
+ * Copyright (C) 2018 BMW Car IT GmbH
*/

#include <linux/trace_clock.h>
@@ -10,18 +11,23 @@
#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>

static ulong delay = 100;
-static char test_mode[10] = "irq";
+static char test_mode[12] = "irq";
+static uint burst_size = 1;

-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)");
+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_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)");

static void busy_wait(ulong time)
{
@@ -34,37 +40,132 @@ static void busy_wait(ulong time)
} while ((end - start) < (time * 1000));
}

-static int preemptirq_delay_run(void *data)
+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();
+}

- 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();
+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); \
+ } \
+
+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;
+
+ for (i = 0; i < burst_size; i++)
+ (testfuncs[i % NR_TEST_FUNCS])(i);
return 0;
}

-static int __init preemptirq_delay_init(void)
+static struct task_struct *preemptirq_start_test(void)
{
char task_name[50];
- struct task_struct *test_task;

snprintf(task_name, sizeof(task_name), "%s_test", test_mode);
+ return kthread_run(preemptirq_delay_run, NULL, task_name);
+}
+
+
+static ssize_t trigger_store(struct kobject *kobj, struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ preemptirq_start_test();
+ 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)
+{
+ struct task_struct *test_task;
+ int retval;
+
+ test_task = preemptirq_start_test();
+ retval = PTR_ERR_OR_ZERO(test_task);
+ 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);

- test_task = kthread_run(preemptirq_delay_run, NULL, task_name);
- return PTR_ERR_OR_ZERO(test_task);
+ return retval;
}

static void __exit preemptirq_delay_exit(void)
{
- return;
+ kobject_put(preemptirq_delay_kobj);
}

module_init(preemptirq_delay_init)
--
2.17.1
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