Re: [PATCH v9 21/22] tracing: Add enable_hist/disable_hist triggers

[Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>]

Hi Tom,

On 2015/07/22 1:10, Tom Zanussi wrote:
> Hi Masami,
> 
> On Mon, 2015-07-20 at 23:57 +0900, Masami Hiramatsu wrote:
>> On 2015/07/17 2:22, Tom Zanussi wrote:
>>> Similar to enable_event/disable_event triggers, these triggers enable
>>> and disable the aggregation of events into maps rather than enabling
>>> and disabling their writing into the trace buffer.
>>>
>>> They can be used to automatically start and stop hist triggers based
>>> on a matching filter condition.
>>>
>>> If there's a paused hist trigger on system:event, the following would
>>> start it when the filter condition was hit:
>>>
>>>   # echo enable_hist:system:event [ if filter] > event/trigger
>>>
>>> And the following would disable a running system:event hist trigger:
>>>
>>>   # echo disable_hist:system:event [ if filter] > event/trigger
>>>
>>> See Documentation/trace/events.txt for real examples.
>>
>> Hmm, do we really need this? Since we've already had multiple instances,
>> if someone wants to make histogram separated from event logger, he/she can
>> make another instance for that, and disable/enable event itself.
>>
>> I'm considering if we accept this methods, we'll need to accept another
>> enable/disable triggers for each action too in the future.
>>
> 
> OK, I haven't implemented multiple instances yet, but if I understand
> you correctly, what you're suggesting is that we can accomplish the same
> thing, by setting up a disabled histogram on system:event and then
> simply using the existing enable_event:system:event trigger to turn it
> on.  Likewise the opposite to disable it.

At first I must apologies to be confused, I forgot that the event
trigger is always enabled (activated) even if the event itself is disabled.
And, I meant that the instance of ftrace, ring-buffers and events, so
hist trigger already supports instances.

e.g.
 # mkdir instances/foo
 # echo hist:key=common_pid > instances/foo/events/sched/sched_process_fork/trigger
 # cat events/sched/sched_process_fork/trigger
# Available triggers:
# traceon traceoff snapshot stacktrace enable_event disable_event enable_hist disable_hist hist

So I've thought if the hist trigger is activated *only when* the event is
enabled, we just need the enable/disable_event trigger.

> I guess we need to add the histogram instance name to the syntax of
> enable_event:system:event to be able to make the distinction between a
> histogram and the current behavior of enabling logging.  
> 
> So here's what we currently have.  This sets up a histogram and starts
> it running, and the user cats event/hist to get the results:
> 
> # echo hist:keys=xxx > event1/trigger
> # cat event1/hist
> 
> And separately the existing enable_event trigger, which enables event1
> (starts it logging to the event logger, and has nothing to do with
> histograms) when event2 is hit:
> 
> # echo enable_event:system:event1 > event2/trigger
> 
> So to extend enable_event to support histograms, we need to be able to
> do this, first set up a paused histogram:
> 
> # echo hist:keys=xxx:pause > event1/trigger
> # cat event1/hist
> 
> Which would be enabled via enable_event like this:
> 
> # echo enable_event:system:event1:hist > event2/trigger

Thanks, but I agree that your current approach, enable_hist, is better than this,
since the hist trigger is a special one.

> Of course 'hist' refers to the initial single-instance histogram - if we
> had multiple instances, 'hist' would be replaced by the instance name
> e.g. to set up two different histograms, each with a different filter:
> 
> # echo hist:keys=xxx:pause if filter1 > event1/trigger
> # cat event1/hist
> 
> # echo hist:keys=xxx:pause if filter2 > event1/trigger
> # cat event1/hist2

As I've said, I meant the 'instance' as ftrace's instance.
However, it seems that the multiple instance should have a unique name
(on same ftrace instance :)), so I expect followings.

 # echo hist:name=foo:keys=xxx if filter1 > event1/trigger
 # echo hist:name=bar:keys=yyy if filter2 > event1/trigger

And hist file shows all histograms on the event.

 # cat event1/hist
# trigger info: hist:name=foo:keys=xxx:vals=hitcount:sort=hitcount:size=2048 [active]
....
# trigger info: hist:name=bar:keys=xxx:vals=hitcount:sort=hitcount:size=2048 [active]
....

And if we reuse an instance on another event,

 # echo hist:name=foo:keys=xxx if filter3 > event2/trigger

Of course we cannot mix the single key and the compound keys on same event,
nor different modifiers nor different types (e.g. string v.s. digit).

Thank you,

> 
> To enable the first histogram when event2 is hit:
> 
> # echo enable_event:system:event1:hist > event2/trigger
> 
> And to enable the second histogram when event2 is hit:
> 
> # echo enable_event:system:event1:hist2 > event2/trigger
> 
> Does that align with what you were thinking regarding both instances and
> the enable/disable_event triggers?  If not, some more explanation and
> examples would help ;-)
> 
> Thanks,
> 
> Tom
> 
>> Thank you,
>>
>>>
>>> Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
>>> ---
>>>  include/linux/trace_events.h        |   1 +
>>>  kernel/trace/trace.c                |  11 ++++
>>>  kernel/trace/trace.h                |  32 ++++++++++
>>>  kernel/trace/trace_events_hist.c    | 115 ++++++++++++++++++++++++++++++++++++
>>>  kernel/trace/trace_events_trigger.c |  71 ++++++++++++----------
>>>  5 files changed, 199 insertions(+), 31 deletions(-)
>>>
>>> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
>>> index 0faf48b..0f3ffdd 100644
>>> --- a/include/linux/trace_events.h
>>> +++ b/include/linux/trace_events.h
>>> @@ -411,6 +411,7 @@ enum event_trigger_type {
>>>  	ETT_STACKTRACE		= (1 << 2),
>>>  	ETT_EVENT_ENABLE	= (1 << 3),
>>>  	ETT_EVENT_HIST		= (1 << 4),
>>> +	ETT_HIST_ENABLE		= (1 << 5),
>>>  };
>>>  
>>>  extern int filter_match_preds(struct event_filter *filter, void *rec);
>>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>>> index 16c64a2..c581750 100644
>>> --- a/kernel/trace/trace.c
>>> +++ b/kernel/trace/trace.c
>>> @@ -3761,6 +3761,10 @@ static const char readme_msg[] =
>>>  	"\t   trigger: traceon, traceoff\n"
>>>  	"\t            enable_event:<system>:<event>\n"
>>>  	"\t            disable_event:<system>:<event>\n"
>>> +#ifdef CONFIG_HIST_TRIGGERS
>>> +	"\t            enable_hist:<system>:<event>\n"
>>> +	"\t            disable_hist:<system>:<event>\n"
>>> +#endif
>>>  #ifdef CONFIG_STACKTRACE
>>>  	"\t\t    stacktrace\n"
>>>  #endif
>>> @@ -3836,6 +3840,13 @@ static const char readme_msg[] =
>>>  	"\t    restart a paused hist trigger.\n\n"
>>>  	"\t    The 'clear' param will clear the contents of a running hist\n"
>>>  	"\t    trigger and leave its current paused/active state.\n\n"
>>> +	"\t    The enable_hist and disable_hist triggers can be used to\n"
>>> +	"\t    have one event conditionally start and stop another event's\n"
>>> +	"\t    already-attached hist trigger.  Any number of enable_hist\n"
>>> +	"\t    and disable_hist triggers can be attached to a given event,\n"
>>> +	"\t    allowing that event to kick off and stop aggregations on\n"
>>> +	"\t    a host of other events.  See Documentation/trace/events.txt\n"
>>> +	"\t    for examples.\n"
>>>  #endif
>>>  ;
>>>  
>>> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
>>> index e6cb781..5e2e3b0 100644
>>> --- a/kernel/trace/trace.h
>>> +++ b/kernel/trace/trace.h
>>> @@ -1102,8 +1102,10 @@ extern const struct file_operations event_hist_fops;
>>>  
>>>  #ifdef CONFIG_HIST_TRIGGERS
>>>  extern int register_trigger_hist_cmd(void);
>>> +extern int register_trigger_hist_enable_disable_cmds(void);
>>>  #else
>>>  static inline int register_trigger_hist_cmd(void) { return 0; }
>>> +static inline int register_trigger_hist_enable_disable_cmds(void) { return 0; }
>>>  #endif
>>>  
>>>  extern int register_trigger_cmds(void);
>>> @@ -1121,6 +1123,34 @@ struct event_trigger_data {
>>>  	struct list_head		list;
>>>  };
>>>  
>>> +/* Avoid typos */
>>> +#define ENABLE_EVENT_STR	"enable_event"
>>> +#define DISABLE_EVENT_STR	"disable_event"
>>> +#define ENABLE_HIST_STR		"enable_hist"
>>> +#define DISABLE_HIST_STR	"disable_hist"
>>> +
>>> +struct enable_trigger_data {
>>> +	struct trace_event_file		*file;
>>> +	bool				enable;
>>> +	bool				hist;
>>> +};
>>> +
>>> +extern int event_enable_trigger_print(struct seq_file *m,
>>> +				      struct event_trigger_ops *ops,
>>> +				      struct event_trigger_data *data);
>>> +extern void event_enable_trigger_free(struct event_trigger_ops *ops,
>>> +				      struct event_trigger_data *data);
>>> +extern int event_enable_trigger_func(struct event_command *cmd_ops,
>>> +				     struct trace_event_file *file,
>>> +				     char *glob, char *cmd, char *param);
>>> +extern int event_enable_register_trigger(char *glob,
>>> +					 struct event_trigger_ops *ops,
>>> +					 struct event_trigger_data *data,
>>> +					 struct trace_event_file *file);
>>> +extern void event_enable_unregister_trigger(char *glob,
>>> +					    struct event_trigger_ops *ops,
>>> +					    struct event_trigger_data *test,
>>> +					    struct trace_event_file *file);
>>>  extern void trigger_data_free(struct event_trigger_data *data);
>>>  extern int event_trigger_init(struct event_trigger_ops *ops,
>>>  			      struct event_trigger_data *data);
>>> @@ -1134,6 +1164,8 @@ extern int set_trigger_filter(char *filter_str,
>>>  			      struct event_trigger_data *trigger_data,
>>>  			      struct trace_event_file *file);
>>>  extern int register_event_command(struct event_command *cmd);
>>> +extern int unregister_event_command(struct event_command *cmd);
>>> +extern int register_trigger_hist_enable_disable_cmds(void);
>>>  
>>>  /**
>>>   * struct event_trigger_ops - callbacks for trace event triggers
>>> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
>>> index 4ba7645..6a43611 100644
>>> --- a/kernel/trace/trace_events_hist.c
>>> +++ b/kernel/trace/trace_events_hist.c
>>> @@ -1345,3 +1345,118 @@ __init int register_trigger_hist_cmd(void)
>>>  
>>>  	return ret;
>>>  }
>>> +
>>> +static void
>>> +hist_enable_trigger(struct event_trigger_data *data, void *rec)
>>> +{
>>> +	struct enable_trigger_data *enable_data = data->private_data;
>>> +	struct event_trigger_data *test;
>>> +
>>> +	list_for_each_entry_rcu(test, &enable_data->file->triggers, list) {
>>> +		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
>>> +			if (enable_data->enable)
>>> +				test->paused = false;
>>> +			else
>>> +				test->paused = true;
>>> +			break;
>>> +		}
>>> +	}
>>> +}
>>> +
>>> +static void
>>> +hist_enable_count_trigger(struct event_trigger_data *data, void *rec)
>>> +{
>>> +	if (!data->count)
>>> +		return;
>>> +
>>> +	if (data->count != -1)
>>> +		(data->count)--;
>>> +
>>> +	hist_enable_trigger(data, rec);
>>> +}
>>> +
>>> +static struct event_trigger_ops hist_enable_trigger_ops = {
>>> +	.func			= hist_enable_trigger,
>>> +	.print			= event_enable_trigger_print,
>>> +	.init			= event_trigger_init,
>>> +	.free			= event_enable_trigger_free,
>>> +};
>>> +
>>> +static struct event_trigger_ops hist_enable_count_trigger_ops = {
>>> +	.func			= hist_enable_count_trigger,
>>> +	.print			= event_enable_trigger_print,
>>> +	.init			= event_trigger_init,
>>> +	.free			= event_enable_trigger_free,
>>> +};
>>> +
>>> +static struct event_trigger_ops hist_disable_trigger_ops = {
>>> +	.func			= hist_enable_trigger,
>>> +	.print			= event_enable_trigger_print,
>>> +	.init			= event_trigger_init,
>>> +	.free			= event_enable_trigger_free,
>>> +};
>>> +
>>> +static struct event_trigger_ops hist_disable_count_trigger_ops = {
>>> +	.func			= hist_enable_count_trigger,
>>> +	.print			= event_enable_trigger_print,
>>> +	.init			= event_trigger_init,
>>> +	.free			= event_enable_trigger_free,
>>> +};
>>> +
>>> +static struct event_trigger_ops *
>>> +hist_enable_get_trigger_ops(char *cmd, char *param)
>>> +{
>>> +	struct event_trigger_ops *ops;
>>> +	bool enable;
>>> +
>>> +	enable = (strcmp(cmd, ENABLE_HIST_STR) == 0);
>>> +
>>> +	if (enable)
>>> +		ops = param ? &hist_enable_count_trigger_ops :
>>> +			&hist_enable_trigger_ops;
>>> +	else
>>> +		ops = param ? &hist_disable_count_trigger_ops :
>>> +			&hist_disable_trigger_ops;
>>> +
>>> +	return ops;
>>> +}
>>> +
>>> +static struct event_command trigger_hist_enable_cmd = {
>>> +	.name			= ENABLE_HIST_STR,
>>> +	.trigger_type		= ETT_HIST_ENABLE,
>>> +	.func			= event_enable_trigger_func,
>>> +	.reg			= event_enable_register_trigger,
>>> +	.unreg			= event_enable_unregister_trigger,
>>> +	.get_trigger_ops	= hist_enable_get_trigger_ops,
>>> +	.set_filter		= set_trigger_filter,
>>> +};
>>> +
>>> +static struct event_command trigger_hist_disable_cmd = {
>>> +	.name			= DISABLE_HIST_STR,
>>> +	.trigger_type		= ETT_HIST_ENABLE,
>>> +	.func			= event_enable_trigger_func,
>>> +	.reg			= event_enable_register_trigger,
>>> +	.unreg			= event_enable_unregister_trigger,
>>> +	.get_trigger_ops	= hist_enable_get_trigger_ops,
>>> +	.set_filter		= set_trigger_filter,
>>> +};
>>> +
>>> +static __init void unregister_trigger_hist_enable_disable_cmds(void)
>>> +{
>>> +	unregister_event_command(&trigger_hist_enable_cmd);
>>> +	unregister_event_command(&trigger_hist_disable_cmd);
>>> +}
>>> +
>>> +__init int register_trigger_hist_enable_disable_cmds(void)
>>> +{
>>> +	int ret;
>>> +
>>> +	ret = register_event_command(&trigger_hist_enable_cmd);
>>> +	if (WARN_ON(ret < 0))
>>> +		return ret;
>>> +	ret = register_event_command(&trigger_hist_disable_cmd);
>>> +	if (WARN_ON(ret < 0))
>>> +		unregister_trigger_hist_enable_disable_cmds();
>>> +
>>> +	return ret;
>>> +}
>>> diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
>>> index e80f30b..9490d8f 100644
>>> --- a/kernel/trace/trace_events_trigger.c
>>> +++ b/kernel/trace/trace_events_trigger.c
>>> @@ -338,7 +338,7 @@ __init int register_event_command(struct event_command *cmd)
>>>   * Currently we only unregister event commands from __init, so mark
>>>   * this __init too.
>>>   */
>>> -static __init int unregister_event_command(struct event_command *cmd)
>>> +__init int unregister_event_command(struct event_command *cmd)
>>>  {
>>>  	struct event_command *p, *n;
>>>  	int ret = -ENODEV;
>>> @@ -1052,15 +1052,6 @@ static __init void unregister_trigger_traceon_traceoff_cmds(void)
>>>  	unregister_event_command(&trigger_traceoff_cmd);
>>>  }
>>>  
>>> -/* Avoid typos */
>>> -#define ENABLE_EVENT_STR	"enable_event"
>>> -#define DISABLE_EVENT_STR	"disable_event"
>>> -
>>> -struct enable_trigger_data {
>>> -	struct trace_event_file		*file;
>>> -	bool				enable;
>>> -};
>>> -
>>>  static void
>>>  event_enable_trigger(struct event_trigger_data *data, void *rec)
>>>  {
>>> @@ -1090,14 +1081,16 @@ event_enable_count_trigger(struct event_trigger_data *data, void *rec)
>>>  	event_enable_trigger(data, rec);
>>>  }
>>>  
>>> -static int
>>> -event_enable_trigger_print(struct seq_file *m, struct event_trigger_ops *ops,
>>> -			   struct event_trigger_data *data)
>>> +int event_enable_trigger_print(struct seq_file *m,
>>> +			       struct event_trigger_ops *ops,
>>> +			       struct event_trigger_data *data)
>>>  {
>>>  	struct enable_trigger_data *enable_data = data->private_data;
>>>  
>>>  	seq_printf(m, "%s:%s:%s",
>>> -		   enable_data->enable ? ENABLE_EVENT_STR : DISABLE_EVENT_STR,
>>> +		   enable_data->hist ?
>>> +		   (enable_data->enable ? ENABLE_HIST_STR : DISABLE_HIST_STR) :
>>> +		   (enable_data->enable ? ENABLE_EVENT_STR : DISABLE_EVENT_STR),
>>>  		   enable_data->file->event_call->class->system,
>>>  		   trace_event_name(enable_data->file->event_call));
>>>  
>>> @@ -1114,9 +1107,8 @@ event_enable_trigger_print(struct seq_file *m, struct event_trigger_ops *ops,
>>>  	return 0;
>>>  }
>>>  
>>> -static void
>>> -event_enable_trigger_free(struct event_trigger_ops *ops,
>>> -			  struct event_trigger_data *data)
>>> +void event_enable_trigger_free(struct event_trigger_ops *ops,
>>> +			       struct event_trigger_data *data)
>>>  {
>>>  	struct enable_trigger_data *enable_data = data->private_data;
>>>  
>>> @@ -1161,10 +1153,9 @@ static struct event_trigger_ops event_disable_count_trigger_ops = {
>>>  	.free			= event_enable_trigger_free,
>>>  };
>>>  
>>> -static int
>>> -event_enable_trigger_func(struct event_command *cmd_ops,
>>> -			  struct trace_event_file *file,
>>> -			  char *glob, char *cmd, char *param)
>>> +int event_enable_trigger_func(struct event_command *cmd_ops,
>>> +			      struct trace_event_file *file,
>>> +			      char *glob, char *cmd, char *param)
>>>  {
>>>  	struct trace_event_file *event_enable_file;
>>>  	struct enable_trigger_data *enable_data;
>>> @@ -1173,6 +1164,7 @@ event_enable_trigger_func(struct event_command *cmd_ops,
>>>  	struct trace_array *tr = file->tr;
>>>  	const char *system;
>>>  	const char *event;
>>> +	bool hist = false;
>>>  	char *trigger;
>>>  	char *number;
>>>  	bool enable;
>>> @@ -1197,8 +1189,15 @@ event_enable_trigger_func(struct event_command *cmd_ops,
>>>  	if (!event_enable_file)
>>>  		goto out;
>>>  
>>> -	enable = strcmp(cmd, ENABLE_EVENT_STR) == 0;
>>> +#ifdef CONFIG_HIST_TRIGGERS
>>> +	hist = ((strcmp(cmd, ENABLE_HIST_STR) == 0) ||
>>> +		(strcmp(cmd, DISABLE_HIST_STR) == 0));
>>>  
>>> +	enable = ((strcmp(cmd, ENABLE_EVENT_STR) == 0) ||
>>> +		  (strcmp(cmd, ENABLE_HIST_STR) == 0));
>>> +#else
>>> +	enable = strcmp(cmd, ENABLE_EVENT_STR) == 0;
>>> +#endif
>>>  	trigger_ops = cmd_ops->get_trigger_ops(cmd, trigger);
>>>  
>>>  	ret = -ENOMEM;
>>> @@ -1218,6 +1217,7 @@ event_enable_trigger_func(struct event_command *cmd_ops,
>>>  	INIT_LIST_HEAD(&trigger_data->list);
>>>  	RCU_INIT_POINTER(trigger_data->filter, NULL);
>>>  
>>> +	enable_data->hist = hist;
>>>  	enable_data->enable = enable;
>>>  	enable_data->file = event_enable_file;
>>>  	trigger_data->private_data = enable_data;
>>> @@ -1295,10 +1295,10 @@ event_enable_trigger_func(struct event_command *cmd_ops,
>>>  	goto out;
>>>  }
>>>  
>>> -static int event_enable_register_trigger(char *glob,
>>> -					 struct event_trigger_ops *ops,
>>> -					 struct event_trigger_data *data,
>>> -					 struct trace_event_file *file)
>>> +int event_enable_register_trigger(char *glob,
>>> +				  struct event_trigger_ops *ops,
>>> +				  struct event_trigger_data *data,
>>> +				  struct trace_event_file *file)
>>>  {
>>>  	struct enable_trigger_data *enable_data = data->private_data;
>>>  	struct enable_trigger_data *test_enable_data;
>>> @@ -1308,6 +1308,8 @@ static int event_enable_register_trigger(char *glob,
>>>  	list_for_each_entry_rcu(test, &file->triggers, list) {
>>>  		test_enable_data = test->private_data;
>>>  		if (test_enable_data &&
>>> +		    (test->cmd_ops->trigger_type ==
>>> +		     data->cmd_ops->trigger_type) &&
>>>  		    (test_enable_data->file == enable_data->file)) {
>>>  			ret = -EEXIST;
>>>  			goto out;
>>> @@ -1333,10 +1335,10 @@ out:
>>>  	return ret;
>>>  }
>>>  
>>> -static void event_enable_unregister_trigger(char *glob,
>>> -					    struct event_trigger_ops *ops,
>>> -					    struct event_trigger_data *test,
>>> -					    struct trace_event_file *file)
>>> +void event_enable_unregister_trigger(char *glob,
>>> +				     struct event_trigger_ops *ops,
>>> +				     struct event_trigger_data *test,
>>> +				     struct trace_event_file *file)
>>>  {
>>>  	struct enable_trigger_data *test_enable_data = test->private_data;
>>>  	struct enable_trigger_data *enable_data;
>>> @@ -1346,6 +1348,8 @@ static void event_enable_unregister_trigger(char *glob,
>>>  	list_for_each_entry_rcu(data, &file->triggers, list) {
>>>  		enable_data = data->private_data;
>>>  		if (enable_data &&
>>> +		    (data->cmd_ops->trigger_type ==
>>> +		     test->cmd_ops->trigger_type) &&
>>>  		    (enable_data->file == test_enable_data->file)) {
>>>  			unregistered = true;
>>>  			list_del_rcu(&data->list);
>>> @@ -1365,8 +1369,12 @@ event_enable_get_trigger_ops(char *cmd, char *param)
>>>  	struct event_trigger_ops *ops;
>>>  	bool enable;
>>>  
>>> +#ifdef CONFIG_HIST_TRIGGERS
>>> +	enable = ((strcmp(cmd, ENABLE_EVENT_STR) == 0) ||
>>> +		  (strcmp(cmd, ENABLE_HIST_STR) == 0));
>>> +#else
>>>  	enable = strcmp(cmd, ENABLE_EVENT_STR) == 0;
>>> -
>>> +#endif
>>>  	if (enable)
>>>  		ops = param ? &event_enable_count_trigger_ops :
>>>  			&event_enable_trigger_ops;
>>> @@ -1437,6 +1445,7 @@ __init int register_trigger_cmds(void)
>>>  	register_trigger_snapshot_cmd();
>>>  	register_trigger_stacktrace_cmd();
>>>  	register_trigger_enable_disable_cmds();
>>> +	register_trigger_hist_enable_disable_cmds();
>>>  	register_trigger_hist_cmd();
>>>  
>>>  	return 0;
>>>
>>
>>
> 
> 
> 


-- 
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@hitachi.com