kvm: search_memslots: add simple LRU memslot caching
In typical guest boot workload only 2-3 memslots are used
extensively, and at that it's mostly the same memslot
lookup operation.
Adding LRU cache improves average lookup time from
46 to 28 cycles (~40%) for this workload.
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 231dd94..1a37144 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -353,6 +353,7 @@
struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM];
/* The mapping table from slot id to the index in memslots[]. */
short id_to_index[KVM_MEM_SLOTS_NUM];
+ atomic_t lru_slot;
};
struct kvm {
@@ -790,12 +791,19 @@
static inline struct kvm_memory_slot *
search_memslots(struct kvm_memslots *slots, gfn_t gfn)
{
- struct kvm_memory_slot *memslot;
+ 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)
+ gfn < memslot->base_gfn + memslot->npages) {
+ atomic_set(&slots->lru_slot, memslot - slots->memslots);
return memslot;
+ }
return NULL;
}