From e7d11c7a894986a13817c1c001e1e7668c5c4eb4 Mon Sep 17 00:00:00 2001 From: Xiao Guangrong Date: Fri, 31 May 2013 08:36:27 +0800 Subject: [PATCH] KVM: MMU: zap pages in batch Zap at lease 10 pages before releasing mmu-lock to reduce the overload caused by requiring lock After the patch, kvm_zap_obsolete_pages can forward progress anyway, so update the comments [ It improves the case 0.6% ~ 1% that do kernel building meanwhile read PCI ROM. ] Note: i am not sure that "10" is the best speculative value, i just guessed that '10' can make vcpu do not spend long time on kvm_zap_obsolete_pages and do not cause mmu-lock too hungry. Signed-off-by: Xiao Guangrong Reviewed-by: Marcelo Tosatti Signed-off-by: Gleb Natapov --- arch/x86/kvm/mmu.c | 35 +++++++++++------------------------ 1 file changed, 11 insertions(+), 24 deletions(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 0880b9b425d7..fe9d6f10e7a9 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -4197,14 +4197,18 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot) spin_unlock(&kvm->mmu_lock); } +#define BATCH_ZAP_PAGES 10 static void kvm_zap_obsolete_pages(struct kvm *kvm) { struct kvm_mmu_page *sp, *node; LIST_HEAD(invalid_list); + int batch = 0; restart: list_for_each_entry_safe_reverse(sp, node, &kvm->arch.active_mmu_pages, link) { + int ret; + /* * No obsolete page exists before new created page since * active_mmu_pages is the FIFO list. @@ -4213,28 +4217,6 @@ static void kvm_zap_obsolete_pages(struct kvm *kvm) break; /* - * Do not repeatedly zap a root page to avoid unnecessary - * KVM_REQ_MMU_RELOAD, otherwise we may not be able to - * progress: - * vcpu 0 vcpu 1 - * call vcpu_enter_guest(): - * 1): handle KVM_REQ_MMU_RELOAD - * and require mmu-lock to - * load mmu - * repeat: - * 1): zap root page and - * send KVM_REQ_MMU_RELOAD - * - * 2): if (cond_resched_lock(mmu-lock)) - * - * 2): hold mmu-lock and load mmu - * - * 3): see KVM_REQ_MMU_RELOAD bit - * on vcpu->requests is set - * then return 1 to call - * vcpu_enter_guest() again. - * goto repeat; - * * Since we are reversely walking the list and the invalid * list will be moved to the head, skip the invalid page * can help us to avoid the infinity list walking. @@ -4242,13 +4224,18 @@ static void kvm_zap_obsolete_pages(struct kvm *kvm) if (sp->role.invalid) continue; - if (need_resched() || spin_needbreak(&kvm->mmu_lock)) { + if (batch >= BATCH_ZAP_PAGES && + (need_resched() || spin_needbreak(&kvm->mmu_lock))) { + batch = 0; kvm_mmu_commit_zap_page(kvm, &invalid_list); cond_resched_lock(&kvm->mmu_lock); goto restart; } - if (kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list)) + ret = kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list); + batch += ret; + + if (ret) goto restart; } -- GitLab