linux-kernel - Re: [PATCH -tip] tracing: use defined fields to print formats

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Date:	Tue, 21 Jul 2009 09:09:25 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip] tracing: use defined fields to print formats

Steven Rostedt wrote:
> On Thu, 16 Jul 2009, Lai Jiangshan wrote:
> 
>> It seems that ftrace_format_##call() and ftrace_define_fields_##call()
>> are duplicate more or less.
>>
>> trace_define_field() defines fields and links them into
>> strcut ftrace_event_call. We reuse them to print formats
>> and remove ftrace_format_##call(). It make all things simpler.
>>
>> TRACE_EVENT_FORMAT_NOFILTER is dropped. Because we should
>> "trace_define_field()" fields for all struct ftrace_event_call,
>> even it's no filter.
> 
> OK, I added this and did a diff of the formats before this patch and 
> after the patch. Here they are (with a lot of duplicats cut out).
> 
> [
>   '<' represents the old format
>   '>' represents the new format (with patch applied)
> ]
> 
> 4c4
> < 	field:unsigned short common_type;	offset:0;	size:2;
> ---
>> 	field:int common_type;	offset:0;	size:2;
> 
> We changed the common type from "unsigned short" to "int"?
> 
> 45,46c45,46
> < 	field:char rwbs[6];	offset:32;	size:6;
> < 	field:char comm[TASK_COMM_LEN];	offset:38;	size:16;
> ---
>> 	field:char[6] rwbs;	offset:32;	size:6;
>> 	field:char[TASK_COMM_LEN] comm;	offset:38;	size:16;
> 
> I have several parsers that expect the '[6]' to come after the 
> declaration.
> 
> 
> 390c390
> < print fmt: "type:%u call_site:%lx ptr:%p"
> ---
>> print fmt: type:%u call_site:%lx ptr:%p
> 
> The 'ftrace' events lost their quotes around the print format.
> 
> 394c394
> < 	field:unsigned short common_type;	offset:0;	size:2;
> ---
>> 	field:unsigned char common_type;	offset:0;	size:2;
> 
> And the ftrace events also now use "unsigned char" for the common_type 
> instead of unsigned short?
> 
> 
> 408c408
> < print fmt: "type:%u call_site:%lx ptr:%p req:%lu alloc:%lu flags:%x node:%d"
> ---
>> print fmt: type:%u call_site:%lx ptr:%p req:%lu alloc:%lu flags:%x node:%d
> 
> 423c423
> < print fmt: "%llx->%llx type:%u state:%u"
> ---
>> print fmt: %llx->%llx type:%u state:%u
> 
> 436c436
> < print fmt: "from: %llx to: %llx"
> ---
>> print fmt: from: %llx to: %llx
> 
> 
> Lots more quotes missing (I'll cut out the rest of the diff of quotes 
> missing).
> 
> 447,448c447,448
> < 	field special:char func[TRACE_FUNC_SIZE+1];	offset:16;	size:31;
> < 	field special:char file[TRACE_FUNC_SIZE+1];	offset:47;	size:21;
> ---
>> 	field:char func[TRACE_FUNC_SIZE+1][TRACE_FUNC_SIZE+1] func;	offset:16;	size:31;
>> 	field:char file[TRACE_FUNC_SIZE+1][TRACE_FUNC_SIZE+1] file;	offset:47;	size:21;
> 
> This is interesting.
> 
> 
>> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> 
> I really like the clean up this patch does, but it must not modify the 
> current format of the files unless there is a really good reason to do so.
> 
> Thanks,
> 

I'll fix it.

There're 4 differences:

1) the type of "common_type" is changed.
It's brought by a bug `__common_field(int, type, 1);`
It'll be fixed.

2) Type Item[Len] ==> Type[Len] Item.
(There are the same, )But it can't not be recovered as before.
Because it's brought by `trace_define_field(event_call, #type "[" #len "]", #item,`
I'll fix trace-cmd and make it supports these two style together.

3) double quotation marks for the format is missing.
It'll be fixed.

4) a line in events/ftrace/print/format is missing.
It'll be fixed.

At the end(fixed patch), the only change is "Type Item[Len] ==> Type[Len] Item".

The values of this patch are:
1) A big function ftrace_format_##call() is defined for every event type.
it waste a lot of memory. this patch saves these memory.

2) reduce coupling: ftrace_format_##call() and
ftrace_define_fields_##call() are almost the same.
We need to maintain them together, it's not good design.

The difference between ftrace_format_##call() and
ftrace_define_fields_##call() implies a bug.

Example: `__common_field(int, type, 1);` in
ftrace_define_fields_##call() is a bug.

Thank you.

Lai.

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