• Jay Zhou's avatar
    KVM: x86: enable dirty log gradually in small chunks · 3c9bd400
    Jay Zhou authored
    It could take kvm->mmu_lock for an extended period of time when
    enabling dirty log for the first time. The main cost is to clear
    all the D-bits of last level SPTEs. This situation can benefit from
    manual dirty log protect as well, which can reduce the mmu_lock
    time taken. The sequence is like this:
    
    1. Initialize all the bits of the dirty bitmap to 1 when enabling
       dirty log for the first time
    2. Only write protect the huge pages
    3. KVM_GET_DIRTY_LOG returns the dirty bitmap info
    4. KVM_CLEAR_DIRTY_LOG will clear D-bit for each of the leaf level
       SPTEs gradually in small chunks
    
    Under the Intel(R) Xeon(R) Gold 6152 CPU @ 2.10GHz environment,
    I did some tests with a 128G windows VM and counted the time taken
    of memory_global_dirty_log_start, here is the numbers:
    
    VM Size        Before    After optimization
    128G           460ms     10ms
    Signed-off-by: default avatarJay Zhou <jianjay.zhou@huawei.com>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    3c9bd400
api.rst 196 KB