[PATCH v2 0/5] KVM: X86: Scaling Guest OS Critical Sections with boosting

[Wanpeng Li]

The missing semantic gap that occurs when a guest OS is preempted 
when executing its own critical section, this leads to degradation 
of application scalability. We try to bridge this semantic gap in 
some ways, by passing guest preempt_count to the host and checking 
guest irq disable state, the hypervisor now knows whether guest 
OSes are running in the critical section, the hypervisor yield-on-spin 
heuristics can be more smart this time to boost the vCPU candidate 
who is in the critical section to mitigate this preemption problem, 
in addition, it is more likely to be a potential lock holder.

Testing on 96 HT 2 socket Xeon CLX server, with 96 vCPUs VM 100GB RAM,
one VM running benchmark, the other(none-2) VMs running cpu-bound 
workloads, There is no performance regression for other benchmarks 
like Unixbench etc.

1VM
            vanilla    optimized    improved

hackbench -l 50000
              28         21.45        30.5%
ebizzy -M
             12189       12354        1.4%
dbench
             712 MB/sec  722 MB/sec   1.4%

2VM:
            vanilla    optimized    improved

hackbench -l 10000
              29.4        26          13%
ebizzy -M
             3834        4033          5%
dbench
           42.3 MB/sec  44.1 MB/sec   4.3%

3VM:
            vanilla    optimized    improved

hackbench -l 10000
              47         35.46        33%
ebizzy -M
	     3828        4031         5%
dbench 
           30.5 MB/sec  31.16 MB/sec  2.3%

v1 -> v2:
 * add more comments to irq disable state 
 * renaming irq_disabled to last_guest_irq_disabled
 * renaming, inverting the return, and also return a bool for kvm_vcpu_non_preemptable

Wanpeng Li (5):
  KVM: X86: Add MSR_KVM_PREEMPT_COUNT support
  KVM: X86: Add last guest interrupt disable state support
  KVM: X86: Boost vCPU which is in critical section
  x86/kvm: Add MSR_KVM_PREEMPT_COUNT guest support
  KVM: X86: Expose PREEMT_COUNT CPUID feature bit to guest

 Documentation/virt/kvm/cpuid.rst     |  3 ++
 arch/x86/include/asm/kvm_host.h      |  8 ++++
 arch/x86/include/uapi/asm/kvm_para.h |  2 +
 arch/x86/kernel/kvm.c                | 10 +++++
 arch/x86/kvm/cpuid.c                 |  3 +-
 arch/x86/kvm/x86.c                   | 60 ++++++++++++++++++++++++++++
 include/linux/kvm_host.h             |  1 +
 virt/kvm/kvm_main.c                  |  7 ++++
 8 files changed, 93 insertions(+), 1 deletion(-)

-- 
2.25.1