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Subject: Re: [PATCH v6] Unified trace buffer
From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
       Thomas Gleixner <tglx@linutronix.de>,
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       Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
       Mike Travis <travis@sgi.com>
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Date: Fri, 26 Sep 2008 21:14:33 +0200
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On Fri, 2008-09-26 at 14:05 -0400, Steven Rostedt wrote:
> +struct ring_buffer {
> +       unsigned long           size;
> +       unsigned                pages;
> +       unsigned                flags;
> +       int                     cpus;
> +       atomic_t                record_disabled;
> +
> +       struct mutex            mutex;
> +
> +       /* FIXME: this should be online CPUS */
> +       struct ring_buffer_per_cpu *buffers[NR_CPUS];

actually nr_possible makes sense, and you might consider always
allocating buffers (and keeping them for offlined cpus) to avoid massive
allocations/frees cpu-hotplug events.

Mike Travis has been going over the kernel removing constructs like
this, and replacing them with dynamically allocated arrays of
nr_possible.

> +};