Re: [PATCH for-5.0 0/4] spapr: Use less XIVE HW resources in KVM

[Greg Kurz]

Oops clumsy fingers, please ignore that ... :)

On Tue, 26 Nov 2019 16:50:38 +0100
Greg Kurz <address@hidden> wrote:

> On POWER9 systems, the XICS-on-XIVE and XIVE KVM devices currently
> allocate a bunch of VPs in the XIVE HW to accomodate the highest
> VCPU id that may be possibly used in a VM. This limits the number
> of VMs that can run with an in-kernel interrupt controller to 63
> per POWER9 chip, irrespectively of its number of HW threads, eg.
> up to 96 on a POWER9 Nimbus socket. This is an unfortunate waste
> of scarce HW resources since a typical VM doesn't need that much
> VPs to run.
> 
> This series exploits new attributes of the XICS-on-XIVE and XIVE
> KVM devices that allow userspace to tune the numbers of VPs it
> really needs.
> 
> Patches 1 to 3 are preliminary work to teach the XICS and XIVE
> backends about the range of needed VCPU ids, according to the
> maximum number of VCPUs specified in the QEMU command line.
> 
> Patch 5 and 6 do the actual work of configuring the KVM devices,
> based on new defines brought by a patch 4. RFC since the patches
> for KVM are still being discussed on the kvm-ppc list:
> 
> https://patchwork.ozlabs.org/project/kvm-ppc/list/?series=132910
> 
> As a bonus, patch 7 allows the latest machine type to automatically
> set int KVM the guest core stride (VSMT) to be equal to the number
> of threads per core (-smp threads=N). This makes VCPU ids contiguous
> and allows to reduce the VP consumption even more.
> 
> Both KVM and QEMU changes are available here:
> https://github.com/gkurz/linux/commits/xive-nr-servers-5.3
> https://github.com/gkurz/qemu/commits/xive-nr-servers-for-4.2
> ---
> 
> Greg Kurz (4):
>       linux-headers: Update
>       spapr: Pass the maximum number of vCPUs to the KVM interrupt controller
>       spapr/xics: Configure number of servers in KVM
>       spapr/xive: Configure number of servers in KVM
> 
> 
>  hw/intc/spapr_xive.c                         |    6 ++++--
>  hw/intc/spapr_xive_kvm.c                     |   26 
> +++++++++++++++++++++++---
>  hw/intc/xics_kvm.c                           |   24 +++++++++++++++++++++---
>  hw/intc/xics_spapr.c                         |    5 +++--
>  hw/ppc/spapr_irq.c                           |    8 +++++---
>  include/hw/ppc/spapr_irq.h                   |   10 ++++++++--
>  include/hw/ppc/spapr_xive.h                  |    3 ++-
>  include/hw/ppc/xics_spapr.h                  |    3 ++-
>  include/standard-headers/linux/ethtool.h     |    6 ++++++
>  include/standard-headers/linux/virtio_ring.h |    2 +-
>  linux-headers/asm-arm/kvm.h                  |    3 ++-
>  linux-headers/asm-arm64/kvm.h                |    5 ++++-
>  linux-headers/asm-mips/unistd_n32.h          |    1 +
>  linux-headers/asm-mips/unistd_n64.h          |    1 +
>  linux-headers/asm-mips/unistd_o32.h          |    1 +
>  linux-headers/asm-powerpc/kvm.h              |    3 +++
>  linux-headers/linux/kvm.h                    |   11 +++++++++++
>  linux-headers/linux/psp-sev.h                |    3 +++
>  18 files changed, 101 insertions(+), 20 deletions(-)
> 
>