linux-kernel - Re: getting processor numbers

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Message-Id: <200704032213.20244.ioe-lkml@rameria.de>
Date:	Tue, 3 Apr 2007 22:13:07 +0200
From:	Ingo Oeser <ioe-lkml@...eria.de>
To:	Ulrich Drepper <drepper@...hat.com>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: getting processor numbers

Hi Ulrich,

On Tuesday 03 April 2007, Ulrich Drepper wrote:
> So, anybody else has a proposal?  This is a pressing issue and cannot
> wait until someday in the distant future NUMA topology information is
> easily and speedily accessible.

Since for now you just need a fast and dirty hack, which will be replaced 
with better interfaces, I suggest creating a directory with some files in it.
These should just contain, what you need to handle your most pressing cases.

I propose /sys/devices/system/topology_counters/ for that.
These can contain "online_cpu", "proped_cpu", "max_cpu"
and maybe the same for nodes. All that as a simple file with an integer
value.

Since sysfs-attribute files are pollable (if the owners notifies sysfs 
on changes), you also have the notification system you need 
(select, poll, epoll etc.).

If you promise to just keep the slow code around, than one day when the shiny 
NUMA topology stuff is ready, this directory can be completely removed and
glibc (plus all their users) keeps working. It will then even work better with a 
new glibc version, which supports the shiny new NUMA topology stuff.

The kernel can create these counters quiete easy, since most of them are 
the hamming weight (or population count) of some bitmaps.

Does this sound like a proper hacky solution? :-)

Regards

Ingo Oeser

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