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Date: Sat, 30 Jan 2010 21:47:38 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
       Steven Rostedt <rostedt@goodmis.org>, Li Zefan <lizf@cn.fujitsu.com>
Subject: Re: [RFC PATCH 05/10] ftrace: Drop buffer check in function
	profiler callbacks
Message-ID: <20100130204737.GF5675@nowhere>
References: <1264122982-1553-1-git-send-regression-fweisbec@gmail.com> <1264122982-1553-6-git-send-regression-fweisbec@gmail.com> <4B5D3779.2040807@cn.fujitsu.com>
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On Mon, Jan 25, 2010 at 02:17:29PM +0800, Lai Jiangshan wrote:
> Frederic Weisbecker wrote:
> > Drop the null check on hlist->hash. It is wasteful because
> > we don't register the tracer if the buffer allocation failed,
> > and the memory barrier in register_ftrace_graph() ensure it
> > is visible to the callbacks right away.
> > 
> 
> When it is on a cpu which is just came up, hlist->hash is not
> allocated either.
> 
> See ftrace_profile_init().
> 
> function_profile_call(), profile_graph_entry() and profile_graph_return()
> on a just online cpu are wasteful. I think we need call
> ftrace_profile_init_cpu()(if ftrace_profile_enabled=1) when CPU_UP_PREPARE.


May be yeah, or perhaps we should play with cpu_possible_mask()
instead of cpu_online. Whatever, the patch is also buggy for the reasons
given by Steve, I'm going to drop it until we have a sane implementation
of synchronize_preempted_tasks().

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