linux-kernel - Re: Re: [PATCH 1/2] tracing: Add $cpu and $current probe-vars

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Date:	Thu, 28 Nov 2013 11:51:18 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung.kim@....com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH 1/2] tracing: Add $cpu and $current probe-vars

(2013/11/28 2:05), Oleg Nesterov wrote:
> On 11/27, Masami Hiramatsu wrote:
>>
>> (2013/11/27 2:23), Oleg Nesterov wrote:
>>> On 11/26, Masami Hiramatsu wrote:
>>>>
>>>> (2013/11/26 4:29), Oleg Nesterov wrote:
>>>>> +#define PSEUDO_REG_OFFSET	4096	/* arbitrary value > MAX_REG_OFFSET */
>>>>> +
>>>>> +static unsigned long probe_get_register(struct pt_regs *regs, unsigned long offset)
>>>>> +{
>>>>> +	if (offset < PSEUDO_REG_OFFSET)
>>>>> +		return regs_get_register(regs, offset);
>>>>> +
>>>>> +	return pseudo_reg_table[offset - PSEUDO_REG_OFFSET].fetch();
>>>>> +}
>>>>
>>>>
>>>> Hmm, I don't like this, since fetch_reg is the most frequently
>>>> used fetch method, and it actually uses the offset in different
>>>> way.
>>>
>>> Sure, this overloads the usage of FETCH_MTD_reg/offset.
>>>
>>> And btw, yes, the naming is ugly (I mean pseudo_*). But why this
>>> is bad? This is cheap and simple.
>>
>> I think it's not simple. The code looks short, but not well
>> self-described. It is "hidden" in the structure, and double-meaning.
> 
> Yes, I agree. And the ugly naming doesn't make it more clear/clean.
> 
> I'll try to cleanup this somehow and resend. Perhaps I should start
> with 2/2 which generalizes FETCH_MTD_reg and kills FETCH_MTD_retval.
> Or at least generalizes FETCH_MTD_retval.

Sounds good for me :)

>>>> Why don't you make another fetch function for vars?
>>>
>>> This is what I tried to avoid ;) I do not want to add another
>>> FETCH_MTD_. To me, this looks like unnecessary complication and
>>> bloat (but see below).
>>
>> I see, perhaps, it is a time to introduce independent fetch
>> method implementation. Current one is not sophisticated
>> nor generic
> 
> Yes, yes, I agree. But until then I do not want to complicate/blow
> this code to implement $current.

Yeah, that is another topic. Let's focus on making it more useful. :)

Thank you,

-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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