linux-kernel - Re: [PATCH 4/4] ring-buffer: only allocate buffers for online cpus

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Message-ID: <alpine.DEB.2.00.0903120925120.3062@gandalf.stny.rr.com>
Date:	Thu, 12 Mar 2009 09:29:30 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Pierre Ossman <drzeus@...eus.cx>, Pekka Paalanen <pq@....fi>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 4/4] ring-buffer: only allocate buffers for online cpus


On Wed, 11 Mar 2009, Andrew Morton wrote:

> On Wed, 11 Mar 2009 22:37:24 -0400 Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > From: Steven Rostedt <srostedt@...hat.com>
> > 
> > Impact: save on memory
> > 
> > Currently, a ring buffer was allocated for each "possible_cpus". On
> > some systems, this is the same as NR_CPUS. Thus, if a system defined
> > NR_CPUS = 64 but it only had 1 CPU, we could have possibly 63 useless
> > ring buffers taking up space. With a default buffer of 3 megs, this
> > could be quite drastic.
> > 
> > This patch changes the ring buffer code to only allocate ring buffers
> > for online CPUs.  If a CPU goes off line, we do not free the buffer.
> > This is because the user may still have trace data in that buffer
> > that they would like to look at.
> > 
> > Perhaps in the future we could add code to delete a ring buffer if
> > the CPU is offline and the ring buffer becomes empty.
> > 
> > ...
> >
> > +#ifdef CONFIG_HOTPLUG
> > +#ifdef CONFIG_HOTPLUG
> > +#ifdef CONFIG_HOTPLUG
> > +#ifdef CONFIG_HOTPLUG
> > +#ifdef CONFIG_HOTPLUG
> 
> CONFIG_HOTPLUG_CPU

Oops, well I did have both in my config to 'y'.

Thanks, will fix.

-- Steve

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