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

[Satheesh Rajendran]

PowerPC KVM guest does not emulate L2 and L2 caches for vCPU, it would be good to have them emulated to guest 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

[Satheesh Rajendran (sathnaga)]

Guest xml(cpu portion):

...
   <vcpu placement='static' current='16'>32</vcpu>
  <resource>
    <partition>/machine</partition>
  </resource>
  <os>
    <type arch='ppc64le' machine='pseries-2.13'>hvm</type>
    <kernel>/home/kvmci/linux/vmlinux</kernel>
    <cmdline>root=/dev/sda2 rw console=tty0 console=ttyS0,115200 init=/sbin/init initcall_debug</cmdline>
    <boot dev='hd'/>
  </os>
  <cpu mode='host-passthrough' check='none'>
    <topology sockets='2' cores='2' threads='8'/>
  </cpu>
...

Host lscpu:
# lscpu
Architecture: ppc64le
Byte Order: Little Endian
CPU(s): 80
On-line CPU(s) list: 0,8,16,24,32,40,48,56,64,72
Off-line CPU(s) list: 1-7,9-15,17-23,25-31,33-39,41-47,49-55,57-63,65-71,73-79
Thread(s) per core: 1
Core(s) per socket: 5
Socket(s): 2
NUMA node(s): 2
Model: 2.1 (pvr 004b 0201)
Model name: POWER8E (raw), altivec supported
CPU max MHz: 3690.0000
CPU min MHz: 2061.0000
L1d cache: 64K
L1i cache: 32K
L2 cache: 512K
L3 cache: 8192K
NUMA node0 CPU(s): 0,8,16,24,32
NUMA node1 CPU(s): 40,48,56,64,72

[Thomas Huth (th-huth)]

The QEMU project is currently considering to move its bug tracking to
another system. For this we need to know which bugs are still valid
and which could be closed already. Thus we are setting older bugs to
"Incomplete" now.

If you still think this bug report here is valid, then please switch
the state back to "New" within the next 60 days, otherwise this report
will be marked as "Expired". Or please mark it as "Fix Released" if
the problem has been solved with a newer version of QEMU already.

Thank you and sorry for the inconvenience.

[Launchpad Janitor (janitor)]

[Expired for QEMU because there has been no activity for 60 days.]