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

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Date:	Fri, 26 Sep 2008 15:28:04 -0700
From:	Mike Travis <travis@....com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Steven Rostedt <rostedt@...dmis.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

Peter Zijlstra wrote:
> 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.
> 
>> +};

The other thing to consider is using a percpu variable.

Cheers,
Mike
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