Re: cpu hotplug

[Gleb Natapov <gleb@redhat.com>]

On Sat, Sep 18, 2010 at 08:27:54PM +0200, Conrad Wood wrote:
> On Sat, 2010-09-18 at 10:32 -0400, Kevin O'Connor wrote:
> > On Fri, Sep 17, 2010 at 11:39:36PM +0200, Conrad Wood wrote:
> > > Hi everyone,
> > > 
> > > I'm currently looking into hotplugging CPUs. 
> > > This exclusively with linux-guests and linux-host.
> > > I have found some (conflicting) information about this on the net.
> > > 
> > > As far as I read:
> > > * seabios doesn't support SMP (but why does the linux-guest show
> > > multiple cpus?)
> > > * there is no uniform way of informing the linux kernel that a cpu has
> > > added (Found references to a unisys way of doing it though, which seems
> > > to be still implemented)
> > > * the kernel needs the acpi tables to determine how many cpus it has,
> > > thus the support in the bios would involve an aml-compiler to
> > > hot-compile new acpi tables.
> > 
> > SeaBIOS version 0.6.1 has ACPI support for cpu-hotplug.  It's been
> > tested on Linux and Windows.  Search the mail archive for "cpu
> > hotplug" for the details.
> > 
> > -Kevin
> > 
> 
> hm... after upgrading to seabios 0.6.1 and qemu-kvm 0.13.50 (git today)
> I get:
> 
> qemu-kvm/hw/qdev.c:94: qdev_create_from_info: Assertion
> `bus->allow_hotplug' failed.
> 
> when I issue cpu_set 4 online on the cmd line. ;(
> 
> starting with commandline:
> 
> /usr/local/kvm/bin/qemu-system-x86_64 -M pc \
> -bios /usr/local/kvm/seabios/latest \
> -cpu phenom -enable-kvm -m 1024 -smp 4,cores=2,maxcpus=30,threads=1
> -name testapp -uuid 5ee3d553-f6a4-0f33-6823-ee16a16a7fb4 -nodefaults \
> -numa 2 \
> -monitor telnet:localhost:9401,server,nowait -rtc base=utc -boot
> ${BOOTSTRAP} -device
> rtl8139,vlan=0,id=net0,mac=52:54:01:65:e6:70,bus=pci.0,addr=0x4 \
> -net tap,ifname=cnw0 -chardev pty,id=serial0 -device
> isa-serial,chardev=serial0 -k en-gb -vga cirrus \
> -drive
> file=/srv/kvm/test-app.qcow2,if=virtio,cache=writeback,bus=0,id=a0,index=0,media=disk,format=qcow2,serial=1,boot=on,snapshot=${SNAPSHOT} \
> -nodefaults \
> -${WD} \
> --enable-nesting \
> 
> 
> any ideas ?
> 
Known problem in qemu. There was a patch for this, but qemu maintainers
think it is not good enough.

--
			Gleb.