[v9,6/7] lib: Add module to simulate atomic sections for testing preemptoff tracers
diff mbox

Message ID 20180628182149.226164-7-joel@joelfernandes.org
State New
Headers show

Commit Message

Joel Fernandes June 28, 2018, 6:21 p.m. UTC
From: "Joel Fernandes (Google)" <joel@joelfernandes.org>

In this patch we introduce a test module for simulating a long atomic
section 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 ./test_atomic_sections.ko atomic_mode=preempt atomic_time=500000
sleep 1
bash-4.3# cat /d/tracing/trace
preempt -1066    2...2    0us@: atomic_sect_run <-atomic_sect_run
preempt -1066    2...2 500002us : atomic_sect_run <-atomic_sect_run
preempt -1066    2...2 500004us : tracer_preempt_on <-atomic_sect_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 ./test_atomic_sections.ko atomic_mode=irq atomic_time=500000
sleep 1
bash-4.3# cat /d/tracing/trace
irq dis -1069    1d..1    0us@: atomic_sect_run
irq dis -1069    1d..1 500001us : atomic_sect_run
irq dis -1069    1d..1 500002us : tracer_hardirqs_on <-atomic_sect_run
irq dis -1069    1d..1 500005us : <stack trace>
 => ret_from_fork

Co-developed-by: Erick Reyes <erickreyes@google.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 lib/Kconfig.debug          |  8 ++++
 lib/Makefile               |  1 +
 lib/test_atomic_sections.c | 77 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 86 insertions(+)
 create mode 100644 lib/test_atomic_sections.c

Comments

Steven Rostedt July 11, 2018, 12:47 a.m. UTC | #1
On Thu, 28 Jun 2018 11:21:48 -0700
Joel Fernandes <joel@joelfernandes.org> wrote:

> From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
> 
> In this patch we introduce a test module for simulating a long atomic
> section 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 ./test_atomic_sections.ko atomic_mode=preempt atomic_time=500000
> sleep 1
> bash-4.3# cat /d/tracing/trace
> preempt -1066    2...2    0us@: atomic_sect_run <-atomic_sect_run
> preempt -1066    2...2 500002us : atomic_sect_run <-atomic_sect_run
> preempt -1066    2...2 500004us : tracer_preempt_on <-atomic_sect_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 ./test_atomic_sections.ko atomic_mode=irq atomic_time=500000
> sleep 1
> bash-4.3# cat /d/tracing/trace
> irq dis -1069    1d..1    0us@: atomic_sect_run
> irq dis -1069    1d..1 500001us : atomic_sect_run
> irq dis -1069    1d..1 500002us : tracer_hardirqs_on <-atomic_sect_run
> irq dis -1069    1d..1 500005us : <stack trace>
>  => ret_from_fork  
> 
> Co-developed-by: Erick Reyes <erickreyes@google.com>
> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> ---
>  lib/Kconfig.debug          |  8 ++++
>  lib/Makefile               |  1 +
>  lib/test_atomic_sections.c | 77 ++++++++++++++++++++++++++++++++++++++

I think this code should reside in kernel/trace directory. I already
have modules there. See the ring_buffer_benchmark code and the test
module for mmio tracer.

>  3 files changed, 86 insertions(+)
>  create mode 100644 lib/test_atomic_sections.c
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 8838d1158d19..622c90e1e066 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1956,6 +1956,14 @@ config TEST_KMOD
>  
>  	  If unsure, say N.
>  
> +config TEST_ATOMIC_SECTIONS
> +	tristate "Simulate atomic sections for tracers to detect"

Hmm, I don't like this title. It's not very obvious to what it is
about. What about "Preempt / IRQ disable delay thread to test latency
tracers" ? Or something along those lines.


> +	depends on m
> +	help
> +	  Select this option to build a test module that can help test atomic
> +	  sections by simulating them with a duration supplied as a module
> +	  parameter. Preempt disable and irq disable modes can be requested.

"If unsure say N"

> +
>  config TEST_DEBUG_VIRTUAL
>  	tristate "Test CONFIG_DEBUG_VIRTUAL feature"
>  	depends on DEBUG_VIRTUAL
> diff --git a/lib/Makefile b/lib/Makefile
> index 90dc5520b784..7831e747bf72 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -44,6 +44,7 @@ obj-y += string_helpers.o
>  obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
>  obj-y += hexdump.o
>  obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
> +obj-$(CONFIG_TEST_ATOMIC_SECTIONS) += test_atomic_sections.o
>  obj-y += kstrtox.o
>  obj-$(CONFIG_FIND_BIT_BENCHMARK) += find_bit_benchmark.o
>  obj-$(CONFIG_TEST_BPF) += test_bpf.o
> diff --git a/lib/test_atomic_sections.c b/lib/test_atomic_sections.c
> new file mode 100644
> index 000000000000..1eef518f0974
> --- /dev/null
> +++ b/lib/test_atomic_sections.c
> @@ -0,0 +1,77 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Atomic section emulation test module
> + *
> + * Emulates atomic sections by disabling IRQs or preemption
> + * and doing a busy wait for a specified amount of time.
> + * This can be used for testing of different atomic section
> + * tracers such as irqsoff tracers.
> + *
> + * (c) 2018. Google LLC
> + */
> +
> +#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 atomic_time = 100;
> +static char atomic_mode[10] = "irq";
> +
> +module_param_named(atomic_time, atomic_time, ulong, S_IRUGO);
> +module_param_string(atomic_mode, atomic_mode, 10, S_IRUGO);
> +MODULE_PARM_DESC(atomic_time, "Period in microseconds (100 uS default)");

It's not a "Period", it's a delay. "Length of time in critical section"

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

  "Mode of the test: preempt or irq disabled (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 atomic_sect_run(void *data)
> +{
> +	unsigned long flags;
> +
> +	if (!strcmp(atomic_mode, "irq")) {
> +		local_irq_save(flags);
> +		busy_wait(atomic_time);
> +		local_irq_restore(flags);
> +	} else if (!strcmp(atomic_mode, "preempt")) {
> +		preempt_disable();
> +		busy_wait(atomic_time);
> +		preempt_enable();
> +	}

So this is a one shot deal? That should be explained somewhere,
probably in the config help message. In fact, I think the config help
message should show how to use this.

-- Steve

> +
> +	return 0;
> +}
> +
> +static int __init atomic_sect_init(void)
> +{
> +	char task_name[50];
> +	struct task_struct *test_task;
> +
> +	snprintf(task_name, sizeof(task_name), "%s_test", atomic_mode);
> +
> +	test_task = kthread_run(atomic_sect_run, NULL, task_name);
> +	return PTR_ERR_OR_ZERO(test_task);
> +}
> +
> +static void __exit atomic_sect_exit(void)
> +{
> +	return;
> +}
> +
> +module_init(atomic_sect_init)
> +module_exit(atomic_sect_exit)
> +MODULE_LICENSE("GPL v2");

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Joel Fernandes July 11, 2018, 5:26 a.m. UTC | #2
On Tue, Jul 10, 2018 at 08:47:07PM -0400, Steven Rostedt wrote:
> On Thu, 28 Jun 2018 11:21:48 -0700
> Joel Fernandes <joel@joelfernandes.org> wrote:
> 
> > From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
> > 
> > In this patch we introduce a test module for simulating a long atomic
> > section 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 ./test_atomic_sections.ko atomic_mode=preempt atomic_time=500000
> > sleep 1
> > bash-4.3# cat /d/tracing/trace
> > preempt -1066    2...2    0us@: atomic_sect_run <-atomic_sect_run
> > preempt -1066    2...2 500002us : atomic_sect_run <-atomic_sect_run
> > preempt -1066    2...2 500004us : tracer_preempt_on <-atomic_sect_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 ./test_atomic_sections.ko atomic_mode=irq atomic_time=500000
> > sleep 1
> > bash-4.3# cat /d/tracing/trace
> > irq dis -1069    1d..1    0us@: atomic_sect_run
> > irq dis -1069    1d..1 500001us : atomic_sect_run
> > irq dis -1069    1d..1 500002us : tracer_hardirqs_on <-atomic_sect_run
> > irq dis -1069    1d..1 500005us : <stack trace>
> >  => ret_from_fork  
> > 
> > Co-developed-by: Erick Reyes <erickreyes@google.com>
> > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> > ---
> >  lib/Kconfig.debug          |  8 ++++
> >  lib/Makefile               |  1 +
> >  lib/test_atomic_sections.c | 77 ++++++++++++++++++++++++++++++++++++++
> 
> I think this code should reside in kernel/trace directory. I already
> have modules there. See the ring_buffer_benchmark code and the test
> module for mmio tracer.

Ok, I'll move it to there.

> >  3 files changed, 86 insertions(+)
> >  create mode 100644 lib/test_atomic_sections.c
> > 
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index 8838d1158d19..622c90e1e066 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -1956,6 +1956,14 @@ config TEST_KMOD
> >  
> >  	  If unsure, say N.
> >  
> > +config TEST_ATOMIC_SECTIONS
> > +	tristate "Simulate atomic sections for tracers to detect"
> 
> Hmm, I don't like this title. It's not very obvious to what it is
> about. What about "Preempt / IRQ disable delay thread to test latency
> tracers" ? Or something along those lines.

Sure, I'll change it to that. I agree its better. I'll change the text to
that and call the config TEST_PREEMPT_IRQ_DISABLE_DELAY.

> > +	depends on m
> > +	help
> > +	  Select this option to build a test module that can help test atomic
> > +	  sections by simulating them with a duration supplied as a module
> > +	  parameter. Preempt disable and irq disable modes can be requested.
> 
> "If unsure say N"

Sure, sounds good.

> > +
> >  config TEST_DEBUG_VIRTUAL
> >  	tristate "Test CONFIG_DEBUG_VIRTUAL feature"
> >  	depends on DEBUG_VIRTUAL
> > diff --git a/lib/Makefile b/lib/Makefile
> > index 90dc5520b784..7831e747bf72 100644
> > --- a/lib/Makefile
> > +++ b/lib/Makefile
> > @@ -44,6 +44,7 @@ obj-y += string_helpers.o
> >  obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
> >  obj-y += hexdump.o
> >  obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
> > +obj-$(CONFIG_TEST_ATOMIC_SECTIONS) += test_atomic_sections.o
> >  obj-y += kstrtox.o
> >  obj-$(CONFIG_FIND_BIT_BENCHMARK) += find_bit_benchmark.o
> >  obj-$(CONFIG_TEST_BPF) += test_bpf.o
> > diff --git a/lib/test_atomic_sections.c b/lib/test_atomic_sections.c
> > new file mode 100644
> > index 000000000000..1eef518f0974
> > --- /dev/null
> > +++ b/lib/test_atomic_sections.c
> > @@ -0,0 +1,77 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Atomic section emulation test module
> > + *
> > + * Emulates atomic sections by disabling IRQs or preemption
> > + * and doing a busy wait for a specified amount of time.
> > + * This can be used for testing of different atomic section
> > + * tracers such as irqsoff tracers.
> > + *
> > + * (c) 2018. Google LLC
> > + */
> > +
> > +#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 atomic_time = 100;
> > +static char atomic_mode[10] = "irq";
> > +
> > +module_param_named(atomic_time, atomic_time, ulong, S_IRUGO);
> > +module_param_string(atomic_mode, atomic_mode, 10, S_IRUGO);
> > +MODULE_PARM_DESC(atomic_time, "Period in microseconds (100 uS default)");
> 
> It's not a "Period", it's a delay. "Length of time in critical section"

Sure.

> > +MODULE_PARM_DESC(atomic_mode, "Mode of the test such as preempt or irq (default irq)");
> 
>   "Mode of the test: preempt or irq disabled (default irq)"

Ok.

> > +
> > +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 atomic_sect_run(void *data)
> > +{
> > +	unsigned long flags;
> > +
> > +	if (!strcmp(atomic_mode, "irq")) {
> > +		local_irq_save(flags);
> > +		busy_wait(atomic_time);
> > +		local_irq_restore(flags);
> > +	} else if (!strcmp(atomic_mode, "preempt")) {
> > +		preempt_disable();
> > +		busy_wait(atomic_time);
> > +		preempt_enable();
> > +	}
> 
> So this is a one shot deal? That should be explained somewhere,
> probably in the config help message. In fact, I think the config help
> message should show how to use this.

Sounds good, I'll clarify it better. Thanks!

- Joel

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Patch
diff mbox

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 8838d1158d19..622c90e1e066 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1956,6 +1956,14 @@  config TEST_KMOD
 
 	  If unsure, say N.
 
+config TEST_ATOMIC_SECTIONS
+	tristate "Simulate atomic sections for tracers to detect"
+	depends on m
+	help
+	  Select this option to build a test module that can help test atomic
+	  sections by simulating them with a duration supplied as a module
+	  parameter. Preempt disable and irq disable modes can be requested.
+
 config TEST_DEBUG_VIRTUAL
 	tristate "Test CONFIG_DEBUG_VIRTUAL feature"
 	depends on DEBUG_VIRTUAL
diff --git a/lib/Makefile b/lib/Makefile
index 90dc5520b784..7831e747bf72 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -44,6 +44,7 @@  obj-y += string_helpers.o
 obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
 obj-y += hexdump.o
 obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
+obj-$(CONFIG_TEST_ATOMIC_SECTIONS) += test_atomic_sections.o
 obj-y += kstrtox.o
 obj-$(CONFIG_FIND_BIT_BENCHMARK) += find_bit_benchmark.o
 obj-$(CONFIG_TEST_BPF) += test_bpf.o
diff --git a/lib/test_atomic_sections.c b/lib/test_atomic_sections.c
new file mode 100644
index 000000000000..1eef518f0974
--- /dev/null
+++ b/lib/test_atomic_sections.c
@@ -0,0 +1,77 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Atomic section emulation test module
+ *
+ * Emulates atomic sections by disabling IRQs or preemption
+ * and doing a busy wait for a specified amount of time.
+ * This can be used for testing of different atomic section
+ * tracers such as irqsoff tracers.
+ *
+ * (c) 2018. Google LLC
+ */
+
+#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 atomic_time = 100;
+static char atomic_mode[10] = "irq";
+
+module_param_named(atomic_time, atomic_time, ulong, S_IRUGO);
+module_param_string(atomic_mode, atomic_mode, 10, S_IRUGO);
+MODULE_PARM_DESC(atomic_time, "Period in microseconds (100 uS default)");
+MODULE_PARM_DESC(atomic_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 atomic_sect_run(void *data)
+{
+	unsigned long flags;
+
+	if (!strcmp(atomic_mode, "irq")) {
+		local_irq_save(flags);
+		busy_wait(atomic_time);
+		local_irq_restore(flags);
+	} else if (!strcmp(atomic_mode, "preempt")) {
+		preempt_disable();
+		busy_wait(atomic_time);
+		preempt_enable();
+	}
+
+	return 0;
+}
+
+static int __init atomic_sect_init(void)
+{
+	char task_name[50];
+	struct task_struct *test_task;
+
+	snprintf(task_name, sizeof(task_name), "%s_test", atomic_mode);
+
+	test_task = kthread_run(atomic_sect_run, NULL, task_name);
+	return PTR_ERR_OR_ZERO(test_task);
+}
+
+static void __exit atomic_sect_exit(void)
+{
+	return;
+}
+
+module_init(atomic_sect_init)
+module_exit(atomic_sect_exit)
+MODULE_LICENSE("GPL v2");