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Subject[PATCH 5/7] KVM: cache the last used slot
Cache the last used slot, the hit ratio is more than 35% during my test

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
include/linux/kvm_host.h | 1 +
virt/kvm/kvm_main.c | 11 +++++++++--
2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f1963a4..7fbae16 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -225,6 +225,7 @@ struct kvm_memslots {
int nmemslots;
int used_slots;
u64 generation;
+ struct kvm_memory_slot *slot_cache;
struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM];
struct kvm_memory_slot *slots_sort[KVM_MEM_SLOTS_NUM];
};
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 0795426..4917d6a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -643,15 +643,21 @@ static struct kvm_memory_slot *search_memslots(struct kvm_memslots *slots,
gfn_t gfn)
{
int start = 0, end = slots->used_slots, idx;
- struct kvm_memory_slot *memslot;
+ struct kvm_memory_slot *memslot = slots->slot_cache;
+
+ if (memslot && gfn >= memslot->base_gfn &&
+ gfn < memslot->base_gfn + memslot->npages)
+ return memslot;

while (start < end) {
idx = (start + end) / 2;
memslot = slots->slots_sort[idx];

if (gfn >= memslot->base_gfn &&
- gfn < memslot->base_gfn + memslot->npages)
+ gfn < memslot->base_gfn + memslot->npages) {
+ slots->slot_cache = memslot;
return memslot;
+ }

if (memslot->base_gfn < gfn)
start = idx + 1;
@@ -684,6 +690,7 @@ void memslots_updated(struct kvm_memslots *slots, int slot_id)
if (slot_id >= slots->nmemslots)
slots->nmemslots = slot_id + 1;
slots->generation++;
+ slots->slot_cache = NULL;
sort_memslots(slots);
}

--
1.7.4


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