linux-kernel - Re: [PATCH v5 2/4] tracing: Add cpu as a key field in histogram

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Date:   Fri, 2 Sep 2016 09:09:52 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Binoy Jayan <binoy.jayan@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Daniel Wagner <daniel.wagner@...-carit.de>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        Masami <masami.hiramatsu@...aro.org>
Subject: Re: [PATCH v5 2/4] tracing: Add cpu as a key field in histogram

On Fri,  2 Sep 2016 18:07:29 +0530
Binoy Jayan <binoy.jayan@...aro.org> wrote:

> The field 'cpu' although part of the set of generic fields, is not made
> part of the key fields when mentioned in the trigger command. This hack
> suggested by Daniel marks it as one of the key fields and make it appear
> in the histogram output.
> 
> Signed-off-by: Binoy Jayan <binoy.jayan@...aro.org>
> ---
>  kernel/trace/trace_events.c      |  3 ++-
>  kernel/trace/trace_events_hist.c | 15 +++++++++++++++
>  2 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 03c0a48..c395608 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -152,7 +152,8 @@ EXPORT_SYMBOL_GPL(trace_define_field);
>  
>  #define __generic_field(type, item, filter_type)			\
>  	ret = __trace_define_field(&ftrace_generic_fields, #type,	\
> -				   #item, 0, 0, is_signed_type(type),	\
> +				   #item, 0, sizeof(type),              \
> +				   is_signed_type(type),                \
>  				   filter_type);			\
>  	if (ret)							\
>  		return ret;
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 0c05b8a..4e0a12e 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -75,6 +75,11 @@ static u64 hist_field_log2(struct hist_field *hist_field, void *event)
>  	return (u64) ilog2(roundup_pow_of_two(val));
>  }
>  
> +static u64 hist_field_cpu(struct hist_field *hist_field, void *event)
> +{
> +	return (u64) raw_smp_processor_id();

Does this really need to be raw? I'm guessing that this would be called
always in preempt disabled locations, but if it is not, wouldn't we
want to know about it?

> +}
> +
>  #define DEFINE_HIST_FIELD_FN(type)					\
>  static u64 hist_field_##type(struct hist_field *hist_field, void *event)\
>  {									\
> @@ -119,6 +124,7 @@ enum hist_field_flags {
>  	HIST_FIELD_FL_SYSCALL		= 128,
>  	HIST_FIELD_FL_STACKTRACE	= 256,
>  	HIST_FIELD_FL_LOG2		= 512,
> +	HIST_FIELD_FL_CPU		= 1024,
>  };
>  
>  struct hist_trigger_attrs {
> @@ -371,6 +377,11 @@ static struct hist_field *create_hist_field(struct ftrace_event_field *field,
>  		goto out;
>  	}
>  
> +	if (flags & HIST_FIELD_FL_CPU) {
> +		hist_field->fn = hist_field_cpu;
> +		goto out;
> +	}
> +
>  	if (WARN_ON_ONCE(!field))
>  		goto out;
>  
> @@ -526,6 +537,9 @@ static int create_key_field(struct hist_trigger_data *hist_data,
>  	} else {
>  		char *field_name = strsep(&field_str, ".");
>  
> +		if (strcmp(field_name, "cpu") == 0)
> +			flags |= HIST_FIELD_FL_CPU;
> +
>  		if (field_str) {
>  			if (strcmp(field_str, "hex") == 0)
>  				flags |= HIST_FIELD_FL_HEX;
> @@ -556,6 +570,7 @@ static int create_key_field(struct hist_trigger_data *hist_data,
>  			key_size = MAX_FILTER_STR_VAL;
>  		else
>  			key_size = field->size;
> +

Unnecessary white space.

-- Steve

>  	}
>  
>  	hist_data->fields[key_idx] = create_hist_field(field, flags);