Hi Sean, > -----Original Message----- > From: Sean Christopherson [mailto:sean.j.christopherson@xxxxxxxxx] > Sent: Wednesday, February 19, 2020 5:23 AM > To: Zhoujian (jay) <jianjay.zhou@xxxxxxxxxx> > Cc: kvm@xxxxxxxxxxxxxxx; pbonzini@xxxxxxxxxx; peterx@xxxxxxxxxx; > wangxin (U) <wangxinxin.wang@xxxxxxxxxx>; linfeng (M) > <linfeng23@xxxxxxxxxx>; Huangweidong (C) <weidong.huang@xxxxxxxxxx> > Subject: Re: [PATCH] KVM: x86: enable dirty log gradually in small chunks > > On Tue, Feb 18, 2020 at 07:00:13PM +0800, Jay Zhou wrote: > > 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. Set all the bits of the first 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@xxxxxxxxxx> > > --- > > arch/x86/kvm/vmx/vmx.c | 5 +++++ > > include/linux/kvm_host.h | 5 +++++ > > virt/kvm/kvm_main.c | 10 ++++++++-- > > 3 files changed, 18 insertions(+), 2 deletions(-) > > > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index > > 3be25ec..a8d64f6 100644 > > --- a/arch/x86/kvm/vmx/vmx.c > > +++ b/arch/x86/kvm/vmx/vmx.c > > @@ -7201,7 +7201,12 @@ static void vmx_sched_in(struct kvm_vcpu *vcpu, > > int cpu) static void vmx_slot_enable_log_dirty(struct kvm *kvm, > > struct kvm_memory_slot *slot) { > > +#if CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT > > + if (!kvm->manual_dirty_log_protect) > > + kvm_mmu_slot_leaf_clear_dirty(kvm, slot); #else > > kvm_mmu_slot_leaf_clear_dirty(kvm, slot); > > +#endif > > The ifdef is unnecessary, this is in VMX (x86) code, i.e. > CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT is guaranteed to be > defined. I agree. > > > kvm_mmu_slot_largepage_remove_write_access(kvm, slot); } > > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index > > e89eb67..fd149b0 100644 > > --- a/include/linux/kvm_host.h > > +++ b/include/linux/kvm_host.h > > @@ -360,6 +360,11 @@ static inline unsigned long > *kvm_second_dirty_bitmap(struct kvm_memory_slot *mem > > return memslot->dirty_bitmap + len / sizeof(*memslot->dirty_bitmap); > > } > > > > +static inline void kvm_set_first_dirty_bitmap(struct kvm_memory_slot > > +*memslot) { > > + bitmap_set(memslot->dirty_bitmap, 0, memslot->npages); } > > I'd prefer this be open coded with a comment, e.g. "first" is misleading because > it's really "initial dirty bitmap for this memslot after enabling dirty logging". kvm_create_dirty_bitmap allocates twice size as large as the actual dirty bitmap size, and there is kvm_second_dirty_bitmap to get the second part of the map, this is the reason why I use first_dirty_bitmap here, which means the first part (not first time) of the dirty bitmap. I'll try to be more clear if this is misleading... > > + > > struct kvm_s390_adapter_int { > > u64 ind_addr; > > u64 summary_addr; > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index > > 70f03ce..08565ed 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -862,7 +862,8 @@ static int kvm_vm_release(struct inode *inode, > struct file *filp) > > * Allocation size is twice as large as the actual dirty bitmap size. > > * See x86's kvm_vm_ioctl_get_dirty_log() why this is needed. > > */ > > -static int kvm_create_dirty_bitmap(struct kvm_memory_slot *memslot) > > +static int kvm_create_dirty_bitmap(struct kvm *kvm, > > + struct kvm_memory_slot *memslot) > > { > > unsigned long dirty_bytes = 2 * kvm_dirty_bitmap_bytes(memslot); > > > > @@ -870,6 +871,11 @@ static int kvm_create_dirty_bitmap(struct > kvm_memory_slot *memslot) > > if (!memslot->dirty_bitmap) > > return -ENOMEM; > > > > +#if CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT > > The ifdef is unnecessary, manual_dirty_log_protect always exists and is > guaranteed to be false if > CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT=n. This isn't exactly a > hot path so saving the uop isn't worth the #ifdef. After rereading the code, I think you're right. > > > + if (kvm->manual_dirty_log_protect) > > + kvm_set_first_dirty_bitmap(memslot); > > +#endif > > + > > return 0; > > } > > > > @@ -1094,7 +1100,7 @@ int __kvm_set_memory_region(struct kvm *kvm, > > > > /* Allocate page dirty bitmap if needed */ > > if ((new.flags & KVM_MEM_LOG_DIRTY_PAGES) && !new.dirty_bitmap) { > > - if (kvm_create_dirty_bitmap(&new) < 0) > > + if (kvm_create_dirty_bitmap(kvm, &new) < 0) > > Rather than pass @kvm, what about doing bitmap_set() in > __kvm_set_memory_region() and > s/kvm_create_dirty_bitmap/kvm_alloc_dirty_bitmap to make it clear that the > helper is only responsible for allocation? And opportunistically drop the > superfluous "< 0", e.g. > > if ((new.flags & KVM_MEM_LOG_DIRTY_PAGES) && !new.dirty_bitmap) { > if (kvm_alloc_dirty_bitmap(&new)) > goto out_free; > > /* > * WORDS! > */ > if (kvm->manual_dirty_log_protect) > bitmap_set(memslot->dirty_bitmap, 0, memslot->npages); > } Seems to be more clear, thanks for the suggestion. Regards, Jay Zhou > > goto out_free; > > } > > > > -- > > 1.8.3.1 > > > >
