From: "Luck, Tony" <tony.luck@intel.com>
To: linux-ia64@vger.kernel.org
Subject: Re: [PATCH] export cpu_sibling_map
Date: Wed, 20 Sep 2006 20:29:35 +0000 [thread overview]
Message-ID: <20060920202935.GA5508@intel.com> (raw)
In-Reply-To: <20060920195347.GD27323@frankl.hpl.hp.com>
On Wed, Sep 20, 2006 at 09:23:25PM +0100, Christoph Hellwig wrote:
> On Wed, Sep 20, 2006 at 12:53:47PM -0700, Stephane Eranian wrote:
> > Hello Tony,
> >
> > For Montecito PMU support, I need to determine, in a kernel module, whether
> > or not threads are enabled. The only reliable way of doing this is to
> > compute the bit-weight of cpu_sibling_map[]. This symbol is exported on
> > x86 systems, but not on IA-64 so far. This patch exports the symbol.
>
> Exporting global variables is a very bad thing, and we only do it if we
> can't avoid it at all. In this case it could be easily avoided by
> exporting a nr_siblings_per_cpu() helper.
I also have my doubts about this in terms of hotplug cpu ... what
do you do if not all of the cpus have their siblings on-line? The
question "Are threads enabled?" doesn't seem to have a simple yes/no
answer. At best you might ask "Does cpu N have any online siblings?"
but the answer to that question could change before you could make
use of the information.
-Tony
next prev parent reply other threads:[~2006-09-20 20:29 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-09-20 19:53 [PATCH] export cpu_sibling_map Stephane Eranian
2006-09-20 20:23 ` Christoph Hellwig
2006-09-20 20:29 ` Luck, Tony [this message]
2006-09-20 20:55 ` Stephane Eranian
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