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KVM: x86: enable dirty log gradually in small chunks

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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: Jay Zhou <jianjay.zhou@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Jay Zhou
2020-02-27 09:32:27 +08:00
committed by Paolo Bonzini
parent 0be4435207
commit 3c9bd4006b
8 changed files with 73 additions and 20 deletions
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3
include/uapi/linux/kvm.h
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@@ -1628,4 +1628,7 @@ struct kvm_hyperv_eventfd {
#define KVM_HYPERV_CONN_ID_MASK 0x00ffffff
#define KVM_HYPERV_EVENTFD_DEASSIGN (1 << 0)
#define KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE (1 << 0)
#define KVM_DIRTY_LOG_INITIALLY_SET (1 << 1)
#endif /* __LINUX_KVM_H */