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RE: [Xen-users] Slightly OT: OS Resource Question

  • To: "Mark Hargrove" <mark@xxxxxxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
  • From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
  • Date: Wed, 8 Mar 2006 11:08:47 +0100
  • Delivery-date: Wed, 08 Mar 2006 10:12:58 +0000
  • List-id: Xen user discussion <xen-users.lists.xensource.com>
  • Thread-index: AcZCQzjZFlDItsZ1QjmP7eOgYlNCVAAU2piQ
  • Thread-topic: [Xen-users] Slightly OT: OS Resource Question

From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Mark Hargrove
Sent: 08 March 2006 00:00
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Slightly OT: OS Resource Question

In principle, can a running Linux kernel recognize the addition of new physical hardware resources such as CPUs, memory, or PCI devices?  Strictly speaking, I'm not asking just about a running Xen instance -- but about a standalone, booted OS.
I'm not an expert on this subject, but I beleive at the moment only by kernel directly supported hotpluggable devices are PCI[xe] devices, USB devices and hard-disks (SCSI, not sure about IDE). That is for a running Linux kernel, and I don't think it matters if it's on top of Xen or not.
Xen allows some trickery that can allow you to make more or less number of CPU's available to the guest by assigning more virtual CPU's than actual CPU's to the guest, and later on move the guest to more or fewer real CPU's. [That is, if I've understood things correctly].
There is the LHCS (Linux Hotplug CPU Support): http://sourceforge.net/projects/lhcs/
This allows the capability of hotplugging CPU's to the Linux kernel - but it's not a part of the kernel itself, it's an external patch.
There's also a patch (which seems both old, kernel 2.6.7 and perhaps incomplete - particularly check out the Known issues description). http://people.valinux.co.jp/~iwamoto/mh.html
And the patch is just disabling/enabling the memory itself, not allowing it to be physically removed/inserted.
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