From: "Joel Fernandes (Google)" joel@joelfernandes.org

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

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 --- kernel/trace/Kconfig | 15 ++++++ kernel/trace/Makefile | 1 + kernel/trace/preemptirq_delay_test.c | 72 ++++++++++++++++++++++++++++ 3 files changed, 88 insertions(+) create mode 100644 kernel/trace/preemptirq_delay_test.c

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index 8d51351e3149..eb5ab6b511e2 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -699,6 +699,21 @@ 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 diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile index 84a0cb222f20..677540bb1b62 100644 --- a/kernel/trace/Makefile +++ b/kernel/trace/Makefile @@ -36,6 +36,7 @@ obj-$(CONFIG_TRACING_MAP) += tracing_map.o obj-$(CONFIG_CONTEXT_SWITCH_TRACER) += trace_sched_switch.o obj-$(CONFIG_FUNCTION_TRACER) += trace_functions.o obj-$(CONFIG_PREEMPTIRQ_TRACEPOINTS) += trace_preemptirq.o +obj-$(CONFIG_PREEMPTIRQ_DELAY_TEST) += preemptirq_delay_test.o obj-$(CONFIG_IRQSOFF_TRACER) += trace_irqsoff.o obj-$(CONFIG_PREEMPT_TRACER) += trace_irqsoff.o obj-$(CONFIG_SCHED_TRACER) += trace_sched_wakeup.o diff --git a/kernel/trace/preemptirq_delay_test.c b/kernel/trace/preemptirq_delay_test.c new file mode 100644 index 000000000000..c97a026c0720 --- /dev/null +++ b/kernel/trace/preemptirq_delay_test.c @@ -0,0 +1,72 @@ +// 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");

From: "Joel Fernandes (Google)" joel@joelfernandes.org

Here we add unit tests for the preemptoff and irqsoff tracer by using a kernel module introduced previously to trigger long preempt or irq disabled sections in the kernel.

Reviewed-by: Masami Hiramatsu mhiramat@kernel.org Acked-by: Masami Hiramatsu mhiramat@kernel.org Signed-off-by: Joel Fernandes (Google) joel@joelfernandes.org --- tools/testing/selftests/ftrace/config | 3 + .../test.d/preemptirq/irqsoff_tracer.tc | 73 +++++++++++++++++++ 2 files changed, 76 insertions(+) create mode 100644 tools/testing/selftests/ftrace/test.d/preemptirq/irqsoff_tracer.tc

diff --git a/tools/testing/selftests/ftrace/config b/tools/testing/selftests/ftrace/config index b01924c71c09..07db5ab09cc7 100644 --- a/tools/testing/selftests/ftrace/config +++ b/tools/testing/selftests/ftrace/config @@ -4,3 +4,6 @@ CONFIG_FUNCTION_PROFILER=y CONFIG_TRACER_SNAPSHOT=y CONFIG_STACK_TRACER=y CONFIG_HIST_TRIGGERS=y +CONFIG_PREEMPT_TRACER=y +CONFIG_IRQSOFF_TRACER=y +CONFIG_PREEMPTIRQ_DELAY_TEST=m diff --git a/tools/testing/selftests/ftrace/test.d/preemptirq/irqsoff_tracer.tc b/tools/testing/selftests/ftrace/test.d/preemptirq/irqsoff_tracer.tc new file mode 100644 index 000000000000..cbd174334a48 --- /dev/null +++ b/tools/testing/selftests/ftrace/test.d/preemptirq/irqsoff_tracer.tc @@ -0,0 +1,73 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# description: test for the preemptirqsoff tracer + +MOD=preemptirq_delay_test + +fail() { + reset_tracer + rmmod $MOD || true + exit_fail +} + +unsup() { #msg + reset_tracer + rmmod $MOD || true + echo $1 + exit_unsupported +} + +modprobe $MOD || unsup "$MOD module not available" +rmmod $MOD + +grep -q "preemptoff" available_tracers || unsup "preemptoff tracer not enabled" +grep -q "irqsoff" available_tracers || unsup "irqsoff tracer not enabled" + +reset_tracer + +# Simulate preemptoff section for half a second couple of times +echo preemptoff > current_tracer +sleep 1 +modprobe $MOD test_mode=preempt delay=500000 || fail +rmmod $MOD || fail +modprobe $MOD test_mode=preempt delay=500000 || fail +rmmod $MOD || fail +modprobe $MOD test_mode=preempt delay=500000 || fail +rmmod $MOD || fail + +cat trace + +# Confirm which tracer +grep -q "tracer: preemptoff" trace || fail + +# Check the end of the section +egrep -q "5.....us : <stack trace>" trace || fail + +# Check for 500ms of latency +egrep -q "latency: 5..... us" trace || fail + +reset_tracer + +# Simulate irqsoff section for half a second couple of times +echo irqsoff > current_tracer +sleep 1 +modprobe $MOD test_mode=irq delay=500000 || fail +rmmod $MOD || fail +modprobe $MOD test_mode=irq delay=500000 || fail +rmmod $MOD || fail +modprobe $MOD test_mode=irq delay=500000 || fail +rmmod $MOD || fail + +cat trace + +# Confirm which tracer +grep -q "tracer: irqsoff" trace || fail + +# Check the end of the section +egrep -q "5.....us : <stack trace>" trace || fail + +# Check for 500ms of latency +egrep -q "latency: 5..... us" trace || fail + +reset_tracer +exit 0