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[Xen-devel] [RFC 0/5] xen/arm: support big.little SoC

From: Peng Fan <peng.fan@xxxxxxx>

This patchset is to support XEN run on big.little SoC.
The idea of the patch is from

There are some changes to cpupool and add x86 stub functions to avoid build
break. Sending The RFC patchset out is to request for comments to see whether
this implementation is acceptable or not. Patchset have been tested based on
xen-4.8 unstable on NXP i.MX8.

I use Big/Little CPU and cpupool to explain the idea.
A pool contains Big CPUs is called Big Pool.
A pool contains Little CPUs is called Little Pool.
If a pool does not contains any physical cpus, Little CPUs or Big CPUs
can be added to the cpupool. But the cpupool can not contain both Little
and Big CPUs. The CPUs in a cpupool must have the same cpu type(midr value for 
CPUs can not be added to the cpupool which contains cpus that have different 
cpu type.
Little CPUs can not be moved to Big Pool if there are Big CPUs in Big Pool,
and versa. Domain in Big Pool can not be migrated to Little Pool, and versa.
When XEN tries to bringup all the CPUs, only add CPUs with the same cpu 
type(same midr value)
into cpupool0.

Thinking an SoC with 4 A53(cpu[0-3]) + 2 A72(cpu[4-5]), cpu0 is the first one
that boots up. When XEN tries to bringup secondary CPUs, add cpu[0-3] to
cpupool0 and leave cpu[4-5] not in any cpupool. Then when Dom0 boots up,
`xl cpupool-list -c` will show cpu[0-3] in Pool-0.

Then use the following script to create a new cpupool and add cpu[4-5] to
the cpupool.
 #xl cpupool-create name=\"Pool-A72\" sched=\"credit2\"
 #xl cpupool-cpu-add Pool-A72 4
 #xl cpupool-cpu-add Pool-A72 5
 #xl create -d /root/xen/domu-test pool=\"Pool-A72\"
Now `xl cpupool-list -c` shows:
Name            CPU list
Pool-0          0,1,2,3 
Pool-A72        4,5

`xl cpupool-list` shows:
Name               CPUs   Sched     Active   Domain count
Pool-0               4    credit       y          1
Pool-A72             2   credit2       y          1

`xl cpupool-cpu-remove Pool-A72 4`, then `xl cpupool-cpu-add Pool-0 4`
not success, because Pool-0 contains A53 CPUs, but CPU4 is an A72 CPU.

`xl cpupool-migrate DomU Pool-0` will also fail, because DomU is created
in Pool-A72 with A72 vcpu, while Pool-0 have A53 physical cpus.

Patch 1/5:
use "cpumask_weight(cpupool0->cpu_valid);" to replace "num_online_cpus()",
because num_online_cpus() counts all the online CPUs, but now we only
need Big or Little CPUs.

Patch 2/5:
Introduce cpupool_arch_info. To ARM SoC, need to add midr info to the cpupool.
The info will be used in patch [3,4,5]/5.

Patch 3/5:
Need to check whether it is ok to add a physical cpu to a cpupool,
When the cpupool does not contain any physical cpus, it is ok
to add a cpu to the cpupool without care the cpu type.
Need to check whether it is ok to move a domain to another cpupool.

Patch 4/5:
move vpidr from arch_domain to arch_vcpu.
The vpidr in arch_domain is initialized in arch_domain_create,
at this time, the domain is still in cpupool0, not moved the specified
cpupool. We need to initialize vpidr later. But at the late stage,
no method to initialize vpidr in arch_domain, so I move it to

Patch 5/5:
This is to check whether it is ok to move a domain to another cpupool.

Peng Fan (5):
  xen/arm: domain_build: setting opt_dom0_max_vcpus according to
    cpupool0 info
  xen: cpupool: introduce cpupool_arch_info
  xen: cpupool: add arch cpupool hook
  xen/arm: move vpidr from arch_domain to arch_vcpu
  xen/arm: cpupool: implement arch_domain_cpupool_compatible

 xen/arch/arm/Makefile         |  1 +
 xen/arch/arm/cpupool.c        | 60 +++++++++++++++++++++++++++++++++++++++++++
 xen/arch/arm/domain.c         |  9 ++++---
 xen/arch/arm/domain_build.c   |  3 ++-
 xen/arch/arm/traps.c          |  2 +-
 xen/arch/x86/cpu/Makefile     |  1 +
 xen/arch/x86/cpu/cpupool.c    | 30 ++++++++++++++++++++++
 xen/common/cpupool.c          | 30 ++++++++++++++++++++++
 xen/include/asm-arm/cpupool.h | 16 ++++++++++++
 xen/include/asm-arm/domain.h  |  9 ++++---
 xen/include/asm-x86/cpupool.h | 16 ++++++++++++
 xen/include/xen/sched-if.h    |  5 ++++
 12 files changed, 173 insertions(+), 9 deletions(-)
 create mode 100644 xen/arch/arm/cpupool.c
 create mode 100644 xen/arch/x86/cpu/cpupool.c
 create mode 100644 xen/include/asm-arm/cpupool.h
 create mode 100644 xen/include/asm-x86/cpupool.h


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