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 atomicsections by simulating them with a duration supplied as a moduleparameter. 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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