Re: [Qemu-devel] [PATCH 0/8] [PATCH RFC v3] s390 cpu hotplug

[Andreas Färber]

Hello,

Am 01.08.2013 16:12, schrieb Jason J. Herne:
> From: "Jason J. Herne" <address@hidden>
> 
> Latest code for cpu Hotplug on S390 architecture.   This one is vastly simpler
> than v2 as we have decided to avoid the command line specification 
> of -device s390-cpu.
> 
> The last version can be found here:
> http://lists.gnu.org/archive/html/qemu-devel/2013-06/msg01183.html
> 
> There is also a patch in this series to add cpu-add to the Qemu monitor
> interface.
> 
> Hotplugged cpus are created in the configured state and can be used by the
> guest after the guest onlines the cpu by: 
> "echo 1 > /sys/bus/cpu/devices/cpuN/online"
> 
> Hot unplugging is currently not implemented by this code. 

We have been having several off-list discussions since then that I'll
try to briefly summarize here, please correct or extend as needed:

1) CPU topology for QOM

Physically a System z machine may have an MCM with, e.g., 6 CPUs with 6
cores each. But unlike x86, there is PR/SM, LPAR and possibly z/VM in
between Linux and hardware, so we do actually want to be able to
hot-plug in quantities of 1 and not by 6 on s390x for the foreseeable
future. We seem willing to set a QOM ABI in stone based on that assumption.

=> s390-cpu (or future subtypes) to be used with device_add.
=> Flat /machine/cpu[n] list in composition tree a possibility.

1a) CPU topology for guests

STSI instruction topology support not implemented yet.

=> Guest unaware of any emulated topology today.

hyptop tool requires hypfs implementation for KVM.

=> Guest unaware of sibling VMs today, unlike z/VM and LPAR.

2) CPU hot-unplug

Hotplug will always use a unique linear CPU address, even if hot-unplug
leads to a sparse address space.

=> cpu_num != cpu_index


With all that in mind, I'll now need to review the s390 patches again.

For the HMP patch I am waiting on feedback from Igor once he returns
from his vacation and, if there are no objections, would like to see
that patch go through Luiz' queue since unrelated to s390x.

Regards,
Andreas

> 
> Jason J. Herne (8):
>   s390-qemu: cpu hotplug - Define New SCLP Codes
>   s390-qemu: cpu hotplug - SCLP CPU Info
>   s390-qemu: cpu hotplug - SCLP Event integration
>   s390-qemu: cpu hotplug - Storage key global access
>   s390-qemu: cpu hotplug - ipi_states enhancements
>   s390-qemu: cpu hotplug - s390 cpu init improvements for hotplug
>   s390-qemu: cpu hotplug - Implement hot_add_cpu hook
>   qemu-monitor: HMP cpu-add wrapper
> 
>  hmp-commands.hx                   |   13 ++++
>  hmp.c                             |   10 ++++
>  hmp.h                             |    1 +
>  hw/s390x/Makefile.objs            |    2 +-
>  hw/s390x/event-facility.c         |    7 +++
>  hw/s390x/s390-virtio-ccw.c        |    8 ++-
>  hw/s390x/s390-virtio.c            |   47 +++++++++------
>  hw/s390x/s390-virtio.h            |    2 +-
>  hw/s390x/sclp.c                   |   53 +++++++++++++++-
>  hw/s390x/sclpcpu.c                |  120 
> +++++++++++++++++++++++++++++++++++++
>  include/hw/s390x/event-facility.h |    3 +
>  include/hw/s390x/sclp.h           |   41 +++++++++++++
>  target-s390x/cpu.c                |   36 ++++++++++-
>  target-s390x/cpu.h                |    7 +++
>  target-s390x/helper.c             |   12 ++++
>  15 files changed, 336 insertions(+), 26 deletions(-)
>  create mode 100644 hw/s390x/sclpcpu.c
> 


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