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Re: [PATCH -v5 08/11] tracing: not trace mips_timecounter_init() in MIPS

To: Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [PATCH -v5 08/11] tracing: not trace mips_timecounter_init() in MIPS
From: Wu Zhangjin <wuzhangjin@gmail.com>
Date: Mon, 09 Nov 2009 12:31:12 +0800
Cc: linux-mips@linux-mips.org, linux-kernel@vger.kernel.org, rostedt@goodmis.org, Thomas Gleixner <tglx@linutronix.de>, Ralf Baechle <ralf@linux-mips.org>, Nicholas Mc Guire <der.herr@hofr.at>, Richard Sandiford <rdsandiford@googlemail.com>, David Daney <ddaney@caviumnetworks.com>, Adam Nemet <anemet@caviumnetworks.com>, Patrik Kluba <kpajko79@gmail.com>
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Reply-to: wuzhangjin@gmail.com
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Hi,

On Mon, 2009-11-02 at 22:43 +0100, Frederic Weisbecker wrote:
[...]
> > > 
> > > But I would rather see a __mips_notrace on these two core functions.
> > 
> > What about this: __arch_notrace? If the arch need this, define it,
> > otherwise, ignore it! if only graph tracer need it, define it in "#ifdef
> > CONFIG_FUNCTION_GRAPH_TRACER ... #endif".
> 
> 
> 
> The problem is that archs may want to disable tracing on different
> places.
> For example mips wants to disable tracing in timecounter_read_delta,
> but another arch may want to disable tracing somewhere else.
> 
> We'll then have several unrelated __arch_notrace. One that is relevant
> for mips, another that is relevant for arch_foo, but all of them will
> apply for all arch that have defined a __arch_notrace.
> 
> It's true that __mips_notrace is not very elegant as it looks like
> a specific arch annotation intruder.
> 
>
> But at least that gives us a per arch filter granularity.
> 
> If only static ftrace could disappear, we could keep only dynamic
> ftrace and we would then be able to filter dynamically.
> But I'm not sure it's a good idea for archs integration.
> 

I think if we use something like __mips_notrace here, we may get lots of
__ARCH_notraces here too, 'Cause some other platforms(at least, as I
know, Microblaze will do it too) may also need to add one here, it will
become:

__mips_notrace __ARCH1_notrace __ARCH2_notrace .... foo() {...}

A little ugly ;)

and If a new platform need it's __ARCH_notrace, they need to touch the
common part of ftrace, more side-effects!

but with __arch_notrace, the archs only need to touch it's own part,
Although there is a side-effect as you mentioned above ;)

So, what should we do?

Regards,
        Wu Zhangjin


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