Re: [rfc] [patch] hook tracer to dynamic debug

[Frederic Weisbecker <fweisbec@gmail.com>]

Hi Jason,


Jason Baron wrote:
> hi,
> 
> Currently, the dynamic debug framework uses 'printk' for output. Here,
> i've hooked the backend of the dynamic debug framework to the tracing 
> framework. This allows the dynamic debug output to be seaprated from the
> system log, and allows for higher performance. I've implemented it as a
> compile time option, but a user might want to be able to toggle b/w
> 'printk' and the tracer at run-time...other ideas? Patch is against the -tip 
> tree...
> 
> thanks,
> 
> -Jason
> 
> 
> diff --git a/include/linux/dynamic_printk.h b/include/linux/dynamic_printk.h
> index 2d528d0..9d9a38b 100644
> --- a/include/linux/dynamic_printk.h
> +++ b/include/linux/dynamic_printk.h
> @@ -31,6 +31,15 @@ struct mod_debug {
>  int register_dynamic_debug_module(char *mod_name, int type, char *share_name,
>  					char *flags, int hash, int hash2);
>  
> +
> +#ifdef CONFIG_DYNAMIC_DEBUG_TRACER
> +#define dynamic_printk dynamic_debug_trace_printk
> +extern void dynamic_debug_trace_printk(const char *fmt, ...);
> +#else
> +#define dynamic_printk printk
> +#endif



Actually, why not directly defining dynamic_printk to ftrace_printk if CONFIG_DYNAMIC_DEBUG_TRACER
is defined?
That would be much simpler than writing a whole tracer for this. I see that one of the pros of this tracer
would be to enable/disable it dynamically by controlling the tracer but you can already do it through
the trace_options file by setting the TRACE_ITER_PRINTK flag.
Unless you just want to get rid of the current ip in the message?


> +
> +
>  #if defined(CONFIG_DYNAMIC_PRINTK_DEBUG)
>  extern int unregister_dynamic_debug_module(char *mod_name);
>  extern int __dynamic_dbg_enabled_helper(char *modname, int type,
> @@ -54,7 +63,7 @@ extern int __dynamic_dbg_enabled_helper(char *modname, int type,
>  	{ mod_name, mod_name, NULL, TYPE_BOOLEAN, DEBUG_HASH, DEBUG_HASH2 };\
>  	if (__dynamic_dbg_enabled(KBUILD_MODNAME, TYPE_BOOLEAN,		    \
>  						0, 0, DEBUG_HASH))	    \
> -		printk(KERN_DEBUG KBUILD_MODNAME ":" fmt,		    \
> +		dynamic_printk(KERN_DEBUG KBUILD_MODNAME ":" fmt,	    \
>  				##__VA_ARGS__);				    \
>  	} while (0)
>  
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index bde6f03..e810912 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -149,6 +149,13 @@ config CONTEXT_SWITCH_TRACER
>  	  This tracer gets called from the context switch and records
>  	  all switching of tasks.
>  
> +config DYNAMIC_DEBUG_TRACER
> +	bool "Trace dynamic debug"
> +	depends on DEBUG_KERNEL
> +	select TRACING
> +	help
> +	  This tracer records all dynamic debug output.
> +
>  config BOOT_TRACER
>  	bool "Trace boot initcalls"
>  	depends on DEBUG_KERNEL
> diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
> index 62dc561..b84337e 100644
> --- a/kernel/trace/Makefile
> +++ b/kernel/trace/Makefile
> @@ -33,5 +33,7 @@ obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += trace_functions_graph.o
>  obj-$(CONFIG_TRACE_BRANCH_PROFILING) += trace_branch.o
>  obj-$(CONFIG_BTS_TRACER) += trace_bts.o
>  obj-$(CONFIG_POWER_TRACER) += trace_power.o
> +obj-$(CONFIG_DYNAMIC_DEBUG_TRACER) += trace_dynamic_debug.o
> +
>  
>  libftrace-y := ftrace.o
> diff --git a/kernel/trace/trace_dynamic_debug.c b/kernel/trace/trace_dynamic_debug.c
> new file mode 100644
> index 0000000..43eaf8a
> --- /dev/null
> +++ b/kernel/trace/trace_dynamic_debug.c
> @@ -0,0 +1,142 @@
> +/*
> + * dynamic_debug tracer
> + *
> + * Copyright (C) 2008 Jason Baron <jbaron@redhat.com>
> + *
> + */
> +#include <linux/module.h>
> +#include <linux/fs.h>
> +#include <linux/debugfs.h>
> +#include <linux/kallsyms.h>
> +#include <linux/uaccess.h>
> +#include <linux/ftrace.h>
> +#include <linux/marker.h>
> +#include <trace/sched.h>
> +
> +#include "trace.h"
> +
> +static struct trace_array	*ctx_trace;
> +static int __read_mostly	debug_enabled;
> +static int			debug_ref;
> +static DEFINE_MUTEX(debug_register_mutex);
> +
> +void dynamic_debug_trace_printk(const char *fmt, ...)
> +{
> +	va_list args;
> +
> +	if (!debug_enabled)
> +		return;
> +
> +	va_start(args, fmt);
> +	trace_vprintk(0, -1, fmt, args);
> +	va_end(args);
> +}
> +EXPORT_SYMBOL(dynamic_debug_trace_printk);
> +
> +static void dynamic_debug_reset(struct trace_array *tr)
> +{
> +	int cpu;
> +
> +	tr->time_start = ftrace_now(tr->cpu);
> +
> +	for_each_online_cpu(cpu)
> +		tracing_reset(tr, cpu);
> +}
> +
> +static void tracing_start_dynamic_debug(void)
> +{
> +	mutex_lock(&debug_register_mutex);
> +	debug_ref++;
> +	mutex_unlock(&debug_register_mutex);
> +}
> +
> +static void tracing_stop_dynamic_debug(void)
> +{
> +	mutex_lock(&debug_register_mutex);
> +	debug_ref--;
> +	mutex_unlock(&debug_register_mutex);
> +}
> +
> +/**
> + * tracing_start_sched_switch_record - start tracing context switches
> + *
> + * Turns on context switch tracing for a tracer.
> + */
> +void tracing_start_dynamic_debug_record(void)
> +{
> +	if (unlikely(!ctx_trace)) {
> +		WARN_ON(1);
> +		return;
> +	}
> +
> +	tracing_start_dynamic_debug();
> +
> +	mutex_lock(&debug_register_mutex);
> +	debug_enabled++;
> +	mutex_unlock(&debug_register_mutex);
> +}
> +
> +/**
> + * tracing_stop_sched_switch_record - start tracing context switches
> + *
> + * Turns off context switch tracing for a tracer.
> + */
> +void tracing_stop_dynamic_debug_record(void)
> +{
> +	mutex_lock(&debug_register_mutex);
> +	debug_enabled--;
> +	WARN_ON(debug_enabled < 0);
> +	mutex_unlock(&debug_register_mutex);
> +
> +	tracing_stop_dynamic_debug();
> +}
> +
> +static void start_dynamic_debug_trace(struct trace_array *tr)
> +{
> +	dynamic_debug_reset(tr);
> +	tracing_start_dynamic_debug_record();
> +}
> +
> +static void stop_dynamic_debug_trace(struct trace_array *tr)
> +{
> +	tracing_stop_dynamic_debug_record();
> +}
> +
> +static int dynamic_debug_trace_init(struct trace_array *tr)
> +{
> +	ctx_trace = tr;
> +	start_dynamic_debug_trace(tr);
> +	return 0;
> +}
> +
> +static void dynamic_debug_trace_reset(struct trace_array *tr)
> +{
> +	if (debug_ref)
> +		stop_dynamic_debug_trace(tr);
> +}
> +
> +static void dynamic_debug_trace_start(struct trace_array *tr)
> +{
> +	dynamic_debug_reset(tr);
> +	tracing_start_dynamic_debug();
> +}
> +
> +static void dynamic_debug_trace_stop(struct trace_array *tr)
> +{
> +	tracing_stop_dynamic_debug();
> +}
> +
> +static struct tracer dynamic_debug_trace __read_mostly =
> +{
> +	.name		= "dynamic_debug",
> +	.init		= dynamic_debug_trace_init,
> +	.reset		= dynamic_debug_trace_reset,
> +	.start		= dynamic_debug_trace_start,
> +	.stop		= dynamic_debug_trace_stop,
> +};
> +
> +__init static int init_dynamic_debug_trace(void)
> +{
> +	return register_tracer(&dynamic_debug_trace);
> +}
> +device_initcall(init_dynamic_debug_trace);
> --
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