linux-kernel - Re: [PATCH v6] Unified trace buffer

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Date:	Fri, 26 Sep 2008 20:18:14 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mike Travis <travis@....com>
cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	prasad@...ux.vnet.ibm.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	David Wilder <dwilder@...ibm.com>, hch@....de,
	Martin Bligh <mbligh@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH v6] Unified trace buffer


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

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