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Date: Fri, 26 Sep 2008 20:18:14 -0400 (EDT)
From: Steven Rostedt <rostedt@goodmis.org>
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To: Mike Travis <travis@sgi.com>
cc: Peter Zijlstra <peterz@infradead.org>, LKML <linux-kernel@vger.kernel.org>,
       Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
       Andrew Morton <akpm@linux-foundation.org>, prasad@linux.vnet.ibm.com,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Mathieu Desnoyers <compudj@krystal.dyndns.org>,
       "Frank Ch. Eigler" <fche@redhat.com>, David Wilder <dwilder@us.ibm.com>,
       hch@lst.de, Martin Bligh <mbligh@google.com>,
       Christoph Hellwig <hch@infradead.org>,
       Masami Hiramatsu <mhiramat@redhat.com>,
       Steven Rostedt <srostedt@redhat.com>,
       Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Subject: Re: [PATCH v6] Unified trace buffer
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On Fri, 26 Sep 2008, Mike Travis wrote:
> Steven Rostedt wrote:
> >> The other thing to consider is using a percpu variable.
> > 
> > This structure is allocated on request.
> > 
> > -- Steve
> 
> 
> Ahh, then it would need the yet to be added cpu_alloc() from Christoph.

We can always change this later.

> 
> Your best bet then is to allocate based on nr_cpu_ids.

Actually in this case I chose num_possible_cpus(). Reason being is that 
later I may add an interface to allow the user to select which CPUs they 
want to trace, and this will only allocate a subset of CPU buffers. 
(not going to implement that in the first release).

But to lay the ground work, I set a buffers->cpumask to be that of all the 
cpus with buffers allocated. For now that mask is set to cpu_possible_map. 
Since num_possible_cpus() is defined as cpus_weight_nr(cpu_possible_map) 
I figured that was the better choice.

-- Steve