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

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Date:	Fri, 26 Sep 2008 20:52:18 -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:
> > 
> > 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
> 
> One problem though, it's *theoretically* possible for num_possible to be
> less than nr_cpu_ids and a cpu index may extend past the end of your
> allocated array.  This would happen if  the cpu indices are allocated
> some other way than as each cpu is discovered.  For example, a system
> might want a group of cpus in one section (say by node, or socket) and
> then a hole in the cpu_possible_map until the next group.  nr_cpu_ids
> is guaranteed to be the highest possible cpu + 1.

Thanks for the explanation. I'll change buffer->cpus to be set to 
nr_cpu_ids.

-- Steve

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