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Commit d4ae84a0 authored by Igor Mammedov's avatar Igor Mammedov Committed by Paolo Bonzini
Browse files

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: default avatarIgor Mammedov <imammedo@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 7f379cff

include/linux/kvm_host.h

+10 −2
Original line number Original line Diff line number Diff line
@@ -353,6 +353,7 @@ struct kvm_memslots { 
	struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM];

	struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM];

	/* The mapping table from slot id to the index in memslots[]. */

	/* The mapping table from slot id to the index in memslots[]. */

	short id_to_index[KVM_MEM_SLOTS_NUM];

	short id_to_index[KVM_MEM_SLOTS_NUM];

	atomic_t lru_slot;

};

};





struct kvm {

struct kvm {
@@ -790,13 +791,20 @@ static inline void kvm_guest_exit(void) 
static inline struct kvm_memory_slot *

static inline struct kvm_memory_slot *

search_memslots(struct kvm_memslots *slots, gfn_t gfn)

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];





	kvm_for_each_memslot(memslot, slots)

	if (gfn >= memslot->base_gfn &&

	if (gfn >= memslot->base_gfn &&

	    gfn < memslot->base_gfn + memslot->npages)

	    gfn < memslot->base_gfn + memslot->npages)

		return memslot;

		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;

		}



	return NULL;

	return NULL;

}

}