linux-kernel - Re: [PATCH] rudimentary tracing for Classic RCU

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Message-ID: <20081009065529.GC24560@one.firstfloor.org>
Date:	Thu, 9 Oct 2008 08:55:29 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	mingo@...e.hu, rjw@...k.pl, dipankar@...ibm.com,
	tglx@...uxtronix.de, andi@...stfloor.org
Subject: Re: [PATCH] rudimentary tracing for Classic RCU

> In this case, why not define it as:
> static char buf[20*NR_CPUS + 100];

Actually you should near never use NR_CPUS now but always num_possible_cpus()
(or even num_online_cpus()) Using NR_CPUS can lead to extreme waste
of memory on kernels which are compiled for 4096 CPUs for example.

And with num_possible_cpus() kmalloc is needed.

-Andi
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