Messages in this thread | | | Date | Mon, 12 Apr 2010 11:43:07 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH 6/6] KVM MMU: optimize synchronization shadow pages |
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On 04/12/2010 11:06 AM, Xiao Guangrong wrote: > - chain all unsync shadow pages then we can fetch them quickly > - flush local/remote tlb after all shadow page synced > > Signed-off-by: Xiao Guangrong<xiaoguangrong@cn.fujitsu.com> > --- > arch/x86/include/asm/kvm_host.h | 1 + > arch/x86/kvm/mmu.c | 82 ++++++++++++++++++--------------------- > 2 files changed, 39 insertions(+), 44 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index d463bc6..ae543fb 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -207,6 +207,7 @@ struct kvm_mmu_page { > #define MMU_PAGE_UNSYNC 0x2 > unsigned int flags; > unsigned int unsync_children; > + struct list_head unsync_link; > union { > u64 *parent_pte; /* !multimapped */ > struct hlist_head parent_ptes; /* multimapped, kvm_pte_chain */ > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index 18eceb2..fcb6299 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -177,6 +177,8 @@ typedef int (*mmu_parent_walk_fn) (struct kvm_mmu_page *sp, u64 *spte); > static struct kmem_cache *pte_chain_cache; > static struct kmem_cache *rmap_desc_cache; > static struct kmem_cache *mmu_page_header_cache; > +static struct list_head unsync_mmu_page_list = > + LIST_HEAD_INIT(unsync_mmu_page_list); > >
Does this really need to be global? Should be per guest.
> static u64 __read_mostly shadow_trap_nonpresent_pte; > static u64 __read_mostly shadow_notrap_nonpresent_pte; > @@ -950,6 +952,7 @@ static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu, > bitmap_zero(sp->slot_bitmap, KVM_MEMORY_SLOTS + KVM_PRIVATE_MEM_SLOTS); > sp->flags = 0; > sp->parent_pte = parent_pte; > + INIT_LIST_HEAD(&sp->unsync_link); > --vcpu->kvm->arch.n_free_mmu_pages; > return sp; > } > @@ -1200,12 +1203,14 @@ static void kvm_unlink_unsync_page(struct kvm *kvm, struct kvm_mmu_page *sp) > { > WARN_ON(!mmu_page_is_unsync(sp)); > mmu_page_clear_unsync(sp); > + list_del(&sp->unsync_link); > --kvm->stat.mmu_unsync; > } >
Locking?
> - if (protected) > - kvm_flush_remote_tlbs(vcpu->kvm); > + if (list_empty(&unsync_mmu_page_list)) > + return; >
Will this ever happen? In my experience we usually have a ton of unsyncs lying around.
> + list_for_each_safe(p, next,&unsync_mmu_page_list) { > + struct kvm_mmu_page *sp; > + sp = list_entry(p, struct kvm_mmu_page, unsync_link); > + __kvm_sync_page(vcpu, sp,&flush_local_tlb,&flush_remote_tlb); > } >
That's counter to the point of unsync. We only want to sync the minimum number of pages - all pages reachable by the new root. The others we want to keep writeable to reduce our fault count.
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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