From: Igor Mammedov Date: Mon, 1 Dec 2014 17:29:27 +0000 (+0000) Subject: kvm: optimize GFN to memslot lookup with large slots amount X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=9c1a5d38780e652275aa55362dbee0d7e827e069;p=deliverable%2Flinux.git kvm: optimize GFN to memslot lookup with large slots amount Current linear search doesn't scale well when large amount of memslots is used and looked up slot is not in the beginning memslots array. Taking in account that memslots don't overlap, it's possible to switch sorting order of memslots array from 'npages' to 'base_gfn' and use binary search for memslot lookup by GFN. As result of switching to binary search lookup times are reduced with large amount of memslots. Following is a table of search_memslot() cycles during WS2008R2 guest boot. boot, boot + ~10 min mostly same of using it, slot lookup randomized lookup max average average cycles cycles cycles 13 slots : 1450 28 30 13 slots : 1400 30 40 binary search 117 slots : 13000 30 460 117 slots : 2000 35 180 binary search Signed-off-by: Igor Mammedov Signed-off-by: Paolo Bonzini --- diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 1a371447fd45..193bca68372d 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -354,6 +354,7 @@ struct kvm_memslots { /* The mapping table from slot id to the index in memslots[]. */ short id_to_index[KVM_MEM_SLOTS_NUM]; atomic_t lru_slot; + int used_slots; }; struct kvm { @@ -791,19 +792,28 @@ static inline void kvm_guest_exit(void) static inline struct kvm_memory_slot * search_memslots(struct kvm_memslots *slots, gfn_t gfn) { + int start = 0, end = slots->used_slots; int slot = atomic_read(&slots->lru_slot); - struct kvm_memory_slot *memslot = &slots->memslots[slot]; - - if (gfn >= memslot->base_gfn && - gfn < memslot->base_gfn + memslot->npages) - return memslot; - - kvm_for_each_memslot(memslot, slots) - if (gfn >= memslot->base_gfn && - gfn < memslot->base_gfn + memslot->npages) { - atomic_set(&slots->lru_slot, memslot - slots->memslots); - return memslot; - } + struct kvm_memory_slot *memslots = slots->memslots; + + if (gfn >= memslots[slot].base_gfn && + gfn < memslots[slot].base_gfn + memslots[slot].npages) + return &memslots[slot]; + + while (start < end) { + slot = start + (end - start) / 2; + + if (gfn >= memslots[slot].base_gfn) + end = slot; + else + start = slot + 1; + } + + if (gfn >= memslots[start].base_gfn && + gfn < memslots[start].base_gfn + memslots[start].npages) { + atomic_set(&slots->lru_slot, start); + return &memslots[start]; + } return NULL; } diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 162817f853ec..759af6596a07 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -679,8 +679,14 @@ static void update_memslots(struct kvm_memslots *slots, struct kvm_memory_slot *mslots = slots->memslots; WARN_ON(mslots[i].id != id); - if (!new->npages) + if (!new->npages) { new->base_gfn = 0; + if (mslots[i].npages) + slots->used_slots--; + } else { + if (!mslots[i].npages) + slots->used_slots++; + } while (i < KVM_MEM_SLOTS_NUM - 1 && new->base_gfn <= mslots[i + 1].base_gfn) {