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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] [patch 2/2] QEMU BOCHS bios patches to use maxcpus value. |
Date: | Sun, 12 Jul 2009 08:23:45 -0500 |
User-agent: | Thunderbird 2.0.0.21 (X11/20090320) |
Avi Kivity wrote:
On 07/10/2009 12:57 AM, Anthony Liguori wrote:These changes make my Ubuntu server guest very unhappy. I get a bunch of messages about "Not responding." on startup.If nothing else, maxcpus ==smp_cpus under QEMU because we don't do CPU hotplug (and I don't think we should).Why shouldn't we do cpu hotplug?
I don't think we should do cpu hotplug via ACPI. I don't think ACPI actually models CPU hotplug and the fact that this works with Linux in KVM is a happy accident. VMware only supports CPU hotplug for Windows 7/2k8 guests so I'm assuming their using Viridian PV extensions to do it.
I think we should go the PV route for Linux too. I'd rather see us create all vcpu threads at once and then let the guest offline each vcpu via a PV notification. I don't see a lot of value in spawning/terminating vcpu threads dynamically and it adds an awful lot of complexity. There's very little overhead to an idle thread.
Regards, Anthony Liguori
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