linux-kernel - Re: [RFC V2 0/9] x86/mmu:Introduce parallel memory virtualization to boost performance

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Date:   Wed, 9 Sep 2020 11:04:26 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Yulei Zhang <yulei.kernel@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Jim Mattson <jmattson@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Ben Gardon <bgardon@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Haiwei Li <lihaiwei.kernel@...il.com>
Subject: Re: [RFC V2 0/9] x86/mmu:Introduce parallel memory virtualization to
 boost performance

Any comments? guys!
On Tue, 1 Sep 2020 at 19:52, <yulei.kernel@...il.com> wrote:
>
> From: Yulei Zhang <yulei.kernel@...il.com>
>
> 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 will cause visible
> performance drop, and it can get worse if guest has more vCPU
> numbers and 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
> simultaneously without page fault exception, thus the performance
> improvement is expected.
>
> We use memory dirty pattern workload to test the initial patch
> set and get positive result even with huge page enabled. For example,
> we create guest with 32 vCPUs and 64G memories, and let the vcpus
> dirty the entire memory region concurrently, as the initial patch
> eliminate the overhead of mmu_lock, in 2M/1G huge page mode we would
> get the job done in about 50% faster.
>
> We only validate this feature on Intel x86 platform. And as Ben
> pointed out in RFC V1, so far we disable the SMM for resource
> consideration, drop the mmu notification as in this case the
> memory is pinned.
>
> V1->V2:
> * Rebase the code to kernel version 5.9.0-rc1.
>
> 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          | 533 ++++++++++++++++++++++++++++++--
>  arch/x86/kvm/svm/svm.c          |   2 +-
>  arch/x86/kvm/vmx/vmx.c          |   7 +-
>  arch/x86/kvm/x86.c              |  55 ++--
>  include/linux/kvm_host.h        |   7 +-
>  virt/kvm/kvm_main.c             |  43 ++-
>  10 files changed, 639 insertions(+), 60 deletions(-)
>
> --
> 2.17.1
>