[0/2] LoongArch: KVM: Add paravirt qspinlock support

Message

Bibo Mao July 23, 2024, 7:38 a.m. UTC

Lock Holder Preemption (LHP) is classic problem especially on VM, if
lock holder vCPU is preempted on host, other vCPUs will do busy looping
and waste pCPU time. And there is no hw Pause Loop Exiting (PLE) supported
on LoongArch system also.

Here pavavirt qspinlock is introduced, by the kernel compiling test, it
improves performance greatly if pVCPU is shared by multiple vCPUs. The
testbed is on 3C5000 Dual-way machine with 32 cores and 2 numa nodes,
test case is kcbench on kernel mainline 5.10, the detailed command is
"kcbench --src /root/src/linux"

Performance on host machine
                      kernel compile time       performance impact
   Original           150.29 seconds
   With patch         150.20 seconds            almost no impact

Performance on virtual machine:
1. 1 VM  with 32 vCPUs and 2 numa node
                      kernel compile time       performance impact
   Original           173.07 seconds
   With patch         171.73 seconds            +1%

2. 2 VMs with 32 vCPUs and 2 numa node
                      kernel compile time       performance impact
   Original           2362.04 seconds
   With patch         354.17 seconds            +566%

Bibo Mao (2):
  LoongArch: KVM: Add paravirt qspinlock in kvm side
  LoongArch: KVM: Add paravirt qspinlock in guest side

 arch/loongarch/Kconfig                        | 14 +++
 arch/loongarch/include/asm/Kbuild             |  1 -
 arch/loongarch/include/asm/kvm_host.h         |  4 +
 arch/loongarch/include/asm/kvm_para.h         |  1 +
 arch/loongarch/include/asm/loongarch.h        |  1 +
 arch/loongarch/include/asm/paravirt.h         | 47 ++++++++++
 arch/loongarch/include/asm/qspinlock.h        | 39 ++++++++
 .../include/asm/qspinlock_paravirt.h          |  6 ++
 arch/loongarch/kernel/paravirt.c              | 88 +++++++++++++++++++
 arch/loongarch/kernel/smp.c                   |  4 +-
 arch/loongarch/kvm/exit.c                     | 24 ++++-
 arch/loongarch/kvm/vcpu.c                     | 13 ++-
 12 files changed, 238 insertions(+), 4 deletions(-)
 create mode 100644 arch/loongarch/include/asm/qspinlock.h
 create mode 100644 arch/loongarch/include/asm/qspinlock_paravirt.h


base-commit: 7846b618e0a4c3e08888099d1d4512722b39ca99