linux-kernel - Re: [PATCH 05/16] tracing: show that buffer size is not expanded

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Message-Id: <20090313114953.43E2.A69D9226@jp.fujitsu.com>
Date:	Fri, 13 Mar 2009 12:05:53 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 05/16] tracing: show that buffer size is not expanded

> From: Steven Rostedt <srostedt@...hat.com>
> 
> Impact: do not confuse user on small trace buffer sizes
> 
> When the system boots up, the trace buffer is small to conserve memory.
> It is only two pages per online CPU. When the tracer is used, it expands
> to the default value.
> 
> This can confuse the user if they look at the buffer size and see only
> 7, but then later they see 1408.
> 
>  # cat /debug/tracing/buffer_size_kb
> 7
> 
>  # echo sched_switch > /debug/tracing/current_tracer
> 
>  # cat /debug/tracing/buffer_size_kb
> 1408
> 
> This patch tries to help remove this confustion by showing that the
> buffer has not been expanded.
> 
>  # cat /debug/tracing/buffer_size_kb
> 7 (expanded: 1408)

Hi,

I have one question.
Why souldn't use following output?

sprintf(buf, "%lu\n", trace_buf_size >> 10);


My point is:
  - pure number output can hadle easily.
  - nobody need to know internal memory saving logic.



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