[Qemu-devel] [Bug 1774605] [NEW] PowerPC guest does not emulate L2 and L3 cache for KVM vCPUs

[Satheesh Rajendran]

Public bug reported:

PowerPC KVM guest does not emulate L2 and L2 caches for vCPU, it would
be good to have them enabled if not any known issues/limitation already
with PowerPC.

Host Env:
kernel: 4.17.0-rc7-00045-g0512e0134582
qemu: v2.12.0-923-gc181ddaa17-dirty
#libvirtd -V
libvirtd (libvirt) 4.4.0


Guest Kernel:
# uname -a
Linux atest-guest 4.17.0-rc7-00045-g0512e0134582 #9 SMP Fri Jun 1 02:55:50 EDT 
2018 ppc64le ppc64le ppc64le GNU/Linux

Guest:
# lscpu
Architecture:        ppc64le
Byte Order:          Little Endian
CPU(s):              16
On-line CPU(s) list: 0-15
Thread(s) per core:  8
Core(s) per socket:  2
Socket(s):           1
NUMA node(s):        1
Model:               2.1 (pvr 004b 0201)
Model name:          POWER8 (architected), altivec supported
Hypervisor vendor:   KVM
Virtualization type: para
L1d cache:           64K
L1i cache:           32K
NUMA node0 CPU(s):   0-15


background: x86 enabling cpu L2 cache bydefault and L3 cache on demand for kvm 
guest
and claims performance improvement as vcpus can be 
benefited with lesser `vmexits due to guest send IPIs.` with L3 cache enabled, 
below was patch for same.

https://git.qemu.org/?p=qemu.git;a=commit;h=14c985cffa6cb177fc01a163d8bcf227c104718c

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1774605

Title:
  PowerPC guest does not emulate L2 and L3 cache for KVM vCPUs

Status in QEMU:
  New

Bug description:
  PowerPC KVM guest does not emulate L2 and L2 caches for vCPU, it would
  be good to have them enabled if not any known issues/limitation
  already with PowerPC.

  Host Env:
  kernel: 4.17.0-rc7-00045-g0512e0134582
  qemu: v2.12.0-923-gc181ddaa17-dirty
  #libvirtd -V
  libvirtd (libvirt) 4.4.0

  
  Guest Kernel:
  # uname -a
  Linux atest-guest 4.17.0-rc7-00045-g0512e0134582 #9 SMP Fri Jun 1 02:55:50 
EDT 2018 ppc64le ppc64le ppc64le GNU/Linux

  Guest:
  # lscpu
  Architecture:        ppc64le
  Byte Order:          Little Endian
  CPU(s):              16
  On-line CPU(s) list: 0-15
  Thread(s) per core:  8
  Core(s) per socket:  2
  Socket(s):           1
  NUMA node(s):        1
  Model:               2.1 (pvr 004b 0201)
  Model name:          POWER8 (architected), altivec supported
  Hypervisor vendor:   KVM
  Virtualization type: para
  L1d cache:           64K
  L1i cache:           32K
  NUMA node0 CPU(s):   0-15


  background: x86 enabling cpu L2 cache bydefault and L3 cache on demand for 
kvm guest
  and claims performance improvement as vcpus can be 
  benefited with lesser `vmexits due to guest send IPIs.` with L3 cache 
enabled, below was patch for same.

  
https://git.qemu.org/?p=qemu.git;a=commit;h=14c985cffa6cb177fc01a163d8bcf227c104718c

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