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

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Message-Id: <1222456474.16700.289.camel@lappy.programming.kicks-ass.net>
Date:	Fri, 26 Sep 2008 21:14:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	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>,
	Mike Travis <travis@....com>
Subject: Re: [PATCH v6] Unified trace buffer

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.

> +};

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