linux-kernel - Re: [RFC PATCH v3 2/4] trace: Add an entry for printing trace log to STM

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Date:	Wed, 8 Jul 2015 16:06:37 +0800
From:	Chunyan Zhang <zhang.chunyan@...aro.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	mingo@...hat.com, Mathieu Poirier <mathieu.poirier@...aro.org>,
	Serge Broslavsky <serge.broslavsky@...aro.org>,
	broonie@...nel.org,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Lyra Zhang <zhang.lyra@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v3 2/4] trace: Add an entry for printing trace log to STM

On Tue, Jul 7, 2015 at 11:58 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Tue,  7 Jul 2015 18:10:41 +0800
> Chunyan Zhang <zhang.chunyan@...aro.org> wrote:
>
>> output_stm is a link which is used to connect trace event
>> logging with STMs, will be used in the upcoming patches.
>>
>> Signed-off-by: Chunyan Zhang <zhang.chunyan@...aro.org>
>> ---
>>  include/linux/trace_events.h | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
>> index 1063c85..28dcdff 100644
>> --- a/include/linux/trace_events.h
>> +++ b/include/linux/trace_events.h
>> @@ -14,6 +14,7 @@ struct trace_buffer;
>>  struct tracer;
>>  struct dentry;
>>  struct bpf_prog;
>> +struct trace_buffer_stm;
>>
>>  struct trace_print_flags {
>>       unsigned long           mask;
>> @@ -293,6 +294,9 @@ struct trace_event_call {
>>        */
>>       int                     flags; /* static flags of different events */
>>
>> +     void (*output_stm)(struct trace_seq *tmp_seq, void *entry,
>> +                        struct trace_buffer_stm *tb);
>> +
>
> Shouldn't the above also have a #ifdef CONFIG_STM_TRACE_EVENT
> encompassing it? Otherwise we are adding 8 bytes to every trace event.
>

Agree. I will address this in the next version of patches.

BTW, in patch 3/4, I defined a structure variable like this:
   "static struct trace_seq *stm_tmp_seq;"
It was actually the first parameter of " trace_event_stm_output_##call
" which was in the patch 4/4.

Do you think if it is an accept way to handle like this? Whether we
would have a better way instead of defining a structure variable
locally?

Thanks,
Chunyan


> -- Steve
>
>>  #ifdef CONFIG_PERF_EVENTS
>>       int                             perf_refcount;
>>       struct hlist_head __percpu      *perf_events;
>> @@ -412,6 +416,10 @@ enum event_trigger_type {
>>       ETT_EVENT_ENABLE        = (1 << 3),
>>  };
>>
>> +#ifdef CONFIG_STM_TRACE_EVENT
>> +extern void stm_trace_event_write(const char *buf, unsigned len);
>> +#endif
>> +
>>  extern int filter_match_preds(struct event_filter *filter, void *rec);
>>
>>  extern int filter_check_discard(struct trace_event_file *file, void *rec,
>
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