On Mon, 13 Apr 2020 20:20:23 +0800
Keqian Zhu <zhukeqian1@xxxxxxxxxx> wrote:
> There is already support of enabling dirty log graually in small chunks
gradually
> for x86 in commit 3c9bd4006bfc ("KVM: x86: enable dirty log gradually in
> small chunks"). This adds support for arm64.
>
> x86 still writes protect all huge pages when DIRTY_LOG_INITIALLY_ALL_SET
> is eanbled. However, for arm64, both huge pages and normal pages can be
enabled
> write protected gradually by userspace.
>
> Under the Huawei Kunpeng 920 2.6GHz platform, I did some tests on 128G
> Linux VMs with different page size. The memory pressure is 127G in each
> case. The time taken of memory_global_dirty_log_start in QEMU is listed
> below:
>
> Page Size Before After Optimization
> 4K 650ms 1.8ms
> 2M 4ms 1.8ms
> 1G 2ms 1.8ms
These numbers are different from what you have advertised before. What
changed?
>
> Besides the time reduction, the biggest income is that we will minimize
s/income/improvement/
> the performance side effect (because of dissloving huge pages and marking
dissolving
> memslots dirty) on guest after enabling dirty log.
>
> Signed-off-by: Keqian Zhu <zhukeqian1@xxxxxxxxxx>
> ---
> Documentation/virt/kvm/api.rst | 2 +-
> arch/arm64/include/asm/kvm_host.h | 3 +++
> virt/kvm/arm/mmu.c | 12 ++++++++++--
> 3 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index efbbe570aa9b..0017f63fa44f 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -5777,7 +5777,7 @@ will be initialized to 1 when created. This also improves performance because
> dirty logging can be enabled gradually in small chunks on the first call
> to KVM_CLEAR_DIRTY_LOG. KVM_DIRTY_LOG_INITIALLY_SET depends on
> KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE (it is also only available on
> -x86 for now).
> +x86 and arm64 for now).
>
> KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 was previously available under the name
> KVM_CAP_MANUAL_DIRTY_LOG_PROTECT, but the implementation had bugs that make
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 32c8a675e5a4..a723f84fab83 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -46,6 +46,9 @@
> #define KVM_REQ_RECORD_STEAL KVM_ARCH_REQ(3)
> #define KVM_REQ_RELOAD_GICv4 KVM_ARCH_REQ(4)
>
> +#define KVM_DIRTY_LOG_MANUAL_CAPS (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \
> + KVM_DIRTY_LOG_INITIALLY_SET)
> +
> DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
>
> extern unsigned int kvm_sve_max_vl;
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index e3b9ee268823..1077f653a611 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -2265,8 +2265,16 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
> * allocated dirty_bitmap[], dirty pages will be be tracked while the
> * memory slot is write protected.
> */
> - if (change != KVM_MR_DELETE && mem->flags & KVM_MEM_LOG_DIRTY_PAGES)
> - kvm_mmu_wp_memory_region(kvm, mem->slot);
> + if (change != KVM_MR_DELETE && mem->flags & KVM_MEM_LOG_DIRTY_PAGES) {
> + /*
> + * If we're with initial-all-set, we don't need to write
> + * protect any pages because they're all reported as dirty.
> + * Huge pages and normal pages will be write protect gradually.
> + */
> + if (!kvm_dirty_log_manual_protect_and_init_set(kvm)) {
> + kvm_mmu_wp_memory_region(kvm, mem->slot);
> + }
> + }
> }
>
> int kvm_arch_prepare_memory_region(struct kvm *kvm,
As it is, it is pretty good. The one thing that isn't clear to me is
why we have a difference in behaviour between x86 and arm64. What
prevents x86 from having the same behaviour as arm64?
Thanks,
M.
--
Jazz is not dead. It just smells funny...
