linux-kernel - Re: Tracing configuration review

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Message-ID: <4BFCCBB0.6040101@cn.fujitsu.com>
Date:	Wed, 26 May 2010 15:20:16 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	Chase Douglas <chase.douglas@...onical.com>,
	Prasad <prasad@...ux.vnet.ibm.com>,
	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
	Soeren Sandmann <sandmann@...mi.au.dk>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: Tracing configuration review

Pekka Enberg wrote:
> On Tue, May 25, 2010 at 11:13 PM, Frederic Weisbecker
> <fweisbec@...il.com> wrote:
>>> # CONFIG_KMEMTRACE is not set (Kconfig says N if unsure)
>> Deprecated. We have the kmem trace event that are a full replacement now.
>> Pekka, Gabriel, can we remove it now?
> 
> I don't think ftrace supports boot-time tracing which kmemtrace did.

We can do boot-time tracing by passing "trace_event=" kernel parameter.

By passing "ftrace=kmemtrace", kmemtrace can be started when
calling tracer_alloc_buffer(), which is an early_initcall.
While trace events are inititialized as a fs_initcall,  it can
be modified to an early_initcall.

Furthermore, I noticed the discussion on perf persistent events, which
seems to enable perf trace at boot time, so I think perf-kmem can take
advantage of this and will be a full-replacement of kmemtrace soon ?

> That said, I was probably the only one actually using the feature so
> maybe we can just nuke kmemtrace at this point...

If you agree on removing kmemtrace now, I'll re-send the patch.

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