linux-kernel - Re: [PATCH 1/2] lib: Add module for testing preemptoff/irqsoff latency tracers

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Date:   Thu, 12 Jul 2018 17:22:32 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Byungchul Park <byungchul.park@....com>,
        Erick Reyes <erickreyes@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Julia Cartwright <julia@...com>,
        linux-kselftest@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Shuah Khan <shuah@...nel.org>,
        Thomas Glexiner <tglx@...utronix.de>,
        Todd Kjos <tkjos@...gle.com>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>
Subject: Re: [PATCH 1/2] lib: Add module for testing preemptoff/irqsoff
 latency tracers

On Tue, 10 Jul 2018 23:35:39 -0700
Joel Fernandes <joel@...lfernandes.org> wrote:

> 
> Co-developed-by: Erick Reyes <erickreyes@...gle.com>

A co-developer needs to add their signed off by. To specify that Erick
is a co-author, you could do:

[ Erick is a co-developer of this commit ]
Signed-off-by: Add Erick's SOB here.

> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.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@...lfernandes.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");