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

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Message-Id: <20090313122458.43EE.A69D9226@jp.fujitsu.com>
Date:	Fri, 13 Mar 2009 12:28:31 +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

> > >  # 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.
> 
> My answer to the second point is: "I do" ;-)
> 
> I like to know the real buffer size. That '7' comes from the ring buffer 
> size directly. If something is going wrong, I do not want to hide the fact 
> that the ring buffer size is not what I expect it to be. Lets say someone 
> modifies the code, and we miss expanding the buffer. It will be very hard 
> to debug why we are getting a small trace. But if we see that the buffer 
> has not been expanded, we know exactly what is wrong.

ok. understanding.
please ignore my last mail.

Thanks!


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