linux-kernel - Re: [PATCH 2/5][RFC] tracing: move function profiler data out of function struct

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Date:	Wed, 25 Mar 2009 11:07:46 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Tim Bird <tim.bird@...sony.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 2/5][RFC] tracing: move function profiler data out of
	function struct


* Steven Rostedt <rostedt@...dmis.org> wrote:

> +/* Interrupts must be disabled calling this */
> +static struct ftrace_profile *
> +ftrace_profile_alloc(unsigned long ip, bool alloc_safe)
> +{
> +	struct ftrace_profile *rec = NULL;
> +
> +	/* prevent recursion */
> +	if (atomic_inc_return(&__get_cpu_var(ftrace_profile_disable)) != 1)
> +		goto out;
> +
> +	__raw_spin_lock(&ftrace_profile_rec_lock);
> +
> +	/* Try to always keep another page available */
> +	if (!profile_pages->next && alloc_safe)
> +		profile_pages->next = (void *)get_zeroed_page(GFP_ATOMIC);

this does not seem to be NMI safe.

This all would be solved much more robustly by the function 
attributes hash approach i suggested in the previous mail. If 
percpu_alloc() is done for 20,000 functions the memory allocation 
overhead is no big deal.

	Ingo
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