[PATCH v5 0/2] x86/kvm: Reduce vcpu_is_preempted() overhead

Waiman Long
2017-02-20T18:36:12Z

v4->v5:
- As suggested by PeterZ, use the asm-offsets header file generation
mechanism to get the offset of the preempted field in
kvm_steal_time instead of hardcoding it.

v3->v4:
- Fix x86-32 build error.

v2->v3:
- Provide an optimized __raw_callee_save___kvm_vcpu_is_preempted()
in assembly as suggested by PeterZ.
- Add a new patch to change vcpu_is_preempted() argument type to long
to ease the writing of the assembly code.

v1->v2:
- Rerun the fio test on a different system on both bare-metal and a
KVM guest. Both sockets were utilized in this test.
- The commit log was updated with new performance numbers, but the
patch wasn't changed.
- Drop patch 2.

As it was found that the overhead of callee-save vcpu_is_preempted()
can have some impact on system performance on a VM guest, especially
of x86-64 guest, this patch set intends to reduce this performance
overhead by replacing the C __kvm_vcpu_is_preempted() function by
an optimized version of __raw_callee_save___kvm_vcpu_is_preempted()
written in assembly.

Waiman Long (2):
x86/paravirt: Change vcp_is_preempted() arg type to long
x86/kvm: Provide optimized version of vcpu_is_preempted() for x86-64

arch/x86/include/asm/paravirt.h | 2 +-
arch/x86/include/asm/qspinlock.h | 2 +-
arch/x86/kernel/asm-offsets_64.c | 9 +++++++++
arch/x86/kernel/kvm.c | 26 +++++++++++++++++++++++++-
arch/x86/kernel/paravirt-spinlocks.c | 2 +-
5 files changed, 37 insertions(+), 4 deletions(-)

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1.8.3.1