Re: [Qemu-devel] [Qemu-ppc] [PATCHv2 0/8] spapr: DRC cleanups (part VI)

[Daniel Henrique Barboza]

On 07/14/2017 03:53 AM, David Gibson wrote:
> On Thu, Jul 13, 2017 at 07:13:23AM -0300, Daniel Henrique Barboza wrote:
> > On 07/12/2017 09:57 PM, David Gibson wrote:
> > > On Wed, Jul 12, 2017 at 10:48:38AM -0300, Daniel Henrique Barboza wrote:
> > > > The dreaded Libvirt hotplug-migrate-hotunplug scenario is working nicely.
> > > Good to hear.
> > >
> > > > device_add when the machine is in RUN_STATE_PRELAUNCH (-S) still doesn't
> > > > work but it is expected - as discussed in "[RFC drcVI PATCH] spapr: reset
> > > > DRCs
> > > > on migration pre_load​", this scenario can't be fixed solely by this DRC
> > > > cleanup.
> > > Hmm.. what's the exact test case you're using here?  The prelaunch
> > > case I tried _did_ work (queueing the event during prelaunch, then
> > > completing the hotplug sequence once the guest had booted).
> > This is the test case:
> >
> > sudo ./qemu-system-ppc64 -name migrate_qemu -boot strict=on --enable-kvm
> > -device nec-usb-xhci,id=usb,bus=pci.0,addr=0xf -device
> > spapr-vscsi,id=scsi0,reg=0x2000 -smp 1,maxcpus=4,sockets=4,cores=1,threads=1
> > --machine pseries,accel=kvm,usb=off,dump-guest-core=off -m
> > 4G,slots=32,maxmem=32G -drive 
> > file=/home/danielhb/vm_imgs/ubuntu1704.qcow2,format=qcow2,if=none,id=drive-virtio-disk0,cache=none
> > -device 
> > virtio-blk-pci,scsi=off,bus=pci.0,addr=0x2,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1
> > -nographic -S
> > QEMU 2.9.50 monitor - type 'help' for more information
> > (qemu)
> > (qemu) device_add host-spapr-cpu-core,id=core1,core-id=1
> > (qemu) cont
> >
> > (...)
> >
> > After OS boots:
> >
> > address@hidden:~$ lscpu
> > Architecture:          ppc64le
> > Byte Order:            Little Endian
> > CPU(s):                1
> > On-line CPU(s) list:   0
> > Thread(s) per core:    1
> > Core(s) per socket:    1
> > Socket(s):             1
> > NUMA node(s):          1
> > Model:                 2.1 (pvr 004b 0201)
> > Model name:            POWER8E (raw), altivec supported
> > Hypervisor vendor:     horizontal
> > Virtualization type:   full
> > L1d cache:             64K
> > L1i cache:             32K
> > NUMA node0 CPU(s):     0
> > address@hidden:~$ (qemu)
> > (qemu) info cpus
> > * CPU #0: nip=0xc0000000000a3e0c thread_id=6134
> >    CPU #1: nip=0x0000000000000000 (halted) thread_id=6163
> > (qemu) info hotpluggable-cpus
> > Hotpluggable CPUs:
> >    type: "host-spapr-cpu-core"
> >    vcpus_count: "1"
> >    CPUInstance Properties:
> >      core-id: "3"
> >    type: "host-spapr-cpu-core"
> >    vcpus_count: "1"
> >    CPUInstance Properties:
> >      core-id: "2"
> >    type: "host-spapr-cpu-core"
> >    vcpus_count: "1"
> >    qom_path: "/machine/peripheral/core1"
> >    CPUInstance Properties:
> >      core-id: "1"
> >    type: "host-spapr-cpu-core"
> >    vcpus_count: "1"
> >    qom_path: "/machine/unattached/device[0]"
> >    CPUInstance Properties:
> >      core-id: "0"
> > (qemu)
> Huh.  I tried basically the same thing, and I get the second cpu once
> the OS is booted.  My first guess would be that the difference is in
> the guest (mine is RHEL 7.3).  Have you double checked that rtas_errd
> and drmgr are present in your guest?

Yeah the guest has drmgr and rtas_errd running. As you said, there might be
something different in the guests that explains why yours work and mine 
doesn't.
Coupling that with the fact that this is not a common usage, I believe we
can leave it as a FYI/reminder if we need to revisit this issue in the
future.


Daniel

> > I am not aware of anyone (e.g. Libvirt) using device_add at that point so
> > it's not
> > urgent to make this work AFAIC. I was just curious of why it
> > doesn't.
> Hm, I thought libvirt did use device_add here in at least some
> circumstances.
>
> I've gone ahead and sent a pull req with the changes, since AFAICT his
> is not a regression, so the DRC cleanups still improve matters
> overall.