Re: [RFC 0/9] KVM:x86/mmu:Introduce parallel memory virtualization to boost performance

[Wanpeng Li]

Also Cc Junaid Shahid, Ben Gardon
On Wed, 5 Aug 2020 at 22:11, Yulei Zhang <yulei.kernel@xxxxxxxxx> wrote:
>
> From: Yulei Zhang <yuleixzhang@xxxxxxxxxxx>
>
> Currently in KVM memory virtulization we relay on mmu_lock to synchronize
> the memory mapping update, which make vCPUs work in serialize mode and
> slow down the execution, especially after migration to do substantial
> memory mapping setup, and performance get worse if increase vCPU numbers
> and guest memories.
>
> The idea we present in this patch set is to mitigate the issue with
> pre-constructed memory mapping table. We will fast pin the guest memory
> to build up a global memory mapping table according to the guest memslots
> changes and apply it to cr3, so that after guest starts up all the vCPUs
> would be able to update the memory concurrently, thus the performance
> improvement is expected.
>
> And after test the initial patch with memory dirty pattern workload, we
> have seen positive results even with huge page enabled. For example,
> guest with 32 vCPUs and 64G memories, in 2M/1G huge page mode we would get
> more than 50% improvement.
>
>
> Yulei Zhang (9):
>   Introduce new fields in kvm_arch/vcpu_arch struct for direct build EPT
>     support
>   Introduce page table population function for direct build EPT feature
>   Introduce page table remove function for direct build EPT feature
>   Add release function for direct build ept when guest VM exit
>   Modify the page fault path to meet the direct build EPT requirement
>   Apply the direct build EPT according to the memory slots change
>   Add migration support when using direct build EPT
>   Introduce kvm module parameter global_tdp to turn on the direct build
>     EPT mode
>   Handle certain mmu exposed functions properly while turn on direct
>     build EPT mode
>
>  arch/mips/kvm/mips.c            |  13 +
>  arch/powerpc/kvm/powerpc.c      |  13 +
>  arch/s390/kvm/kvm-s390.c        |  13 +
>  arch/x86/include/asm/kvm_host.h |  13 +-
>  arch/x86/kvm/mmu/mmu.c          | 537 ++++++++++++++++++++++++++++++--
>  arch/x86/kvm/svm/svm.c          |   2 +-
>  arch/x86/kvm/vmx/vmx.c          |  17 +-
>  arch/x86/kvm/x86.c              |  55 ++--
>  include/linux/kvm_host.h        |   7 +-
>  virt/kvm/kvm_main.c             |  43 ++-
>  10 files changed, 648 insertions(+), 65 deletions(-)
>
> --
> 2.17.1
>