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

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Date:	Fri, 26 Sep 2008 17:05:26 -0700
From:	Mike Travis <travis@....com>
To:	Steven Rostedt <rostedt@...dmis.org>
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

Steven Rostedt wrote:
> On Fri, 26 Sep 2008, Mike Travis wrote:
> 
>> 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.
> 
> This structure is allocated on request.
> 
> -- Steve


Ahh, then it would need the yet to be added cpu_alloc() from Christoph.

Your best bet then is to allocate based on nr_cpu_ids.

Cheers,
Mike
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