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

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Date:	Fri, 10 Oct 2008 04:48:11 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, rjw@...k.pl, dipankar@...ibm.com,
	tglx@...uxtronix.de
Subject: Re: [PATCH] rudimentary tracing for Classic RCU

On Thu, Oct 09, 2008 at 03:05:57PM +0800, Lai Jiangshan wrote:
> Andi Kleen wrote:
> >> 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
> 
> I thought the default value of NR_CPUS is 32.
> 
> if NR_CPUS is too large, I think using seq_file is good idea,
> and rcuclassic_trace_mutex is not need too.

I never have used seq_file, to be honest.  I would welcome a patch from
you applying it to my rcucb and rcudata patch set.

							Thanx, Paul
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