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Re: [Qemu-devel] [patch 2/2] QEMU BOCHS bios patches to use maxcpus valu
Re: [Qemu-devel] [patch 2/2] QEMU BOCHS bios patches to use maxcpus value.
Sun, 12 Jul 2009 08:23:45 -0500
Thunderbird 18.104.22.168 (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.