linux-kernel - Re: cpusets not cpu hotplug aware

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Message-Id: <20060821221145.ff88769f.akpm@osdl.org>
Date:	Mon, 21 Aug 2006 22:11:45 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Nathan Lynch <ntl@...ox.com>
Cc:	Paul Jackson <pj@....com>, Anton Blanchard <anton@...ba.org>,
	simon.derr@...l.net, nathanl@...tin.ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: cpusets not cpu hotplug aware

On Tue, 22 Aug 2006 00:04:01 -0500
Nathan Lynch <ntl@...ox.com> wrote:

> > If the kernel provider (ie: distro) has enabled cpusets then it would be
> > appropriate that they also provide a hotplug script which detects whether their
> > user is actually using cpusets and if not, to take some sensible default action. 
> > ie: add the newly-added CPU to the system's single cpuset, no?
> 
> I think it would be more sensible for the default (i.e. user hasn't
> explicitly configured any cpusets) behavior on a CONFIG_CPUSETS=y
> kernel to match the behavior with a CONFIG_CPUSETS=n kernel.

Well...  why?  If he-who-configured the kernel chose cpusets then it's
reasonable to expect he-who-configures to have appropriate userspace
support for that kernel.

>  Right
> now we don't have that.  Binding a task to a newly added cpu just
> fails if CONFIG_CPUSETS=y, but it works if CONFIG_CPUSETS=n.

Sure.  That's because we're not taking appropriate (ie any) action when a
CPU is added.
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