[PATCH v3 6/6] KVM: introduce a table to map slot id to index in memslots array

[Xiao Guangrong]

From: Xiao Guangrong <xiaoguangr...@linux.vnet.ibm.com>

The operation of getting dirty log is frequent when framebuffer-based
displays are used(for example, Xwindow), so, we introduce a mapping table
to speed up id_to_memslot()

Signed-off-by: Xiao Guangrong <xiaoguangr...@linux.vnet.ibm.com>
---
 include/linux/kvm_host.h |   13 +++++++------
 virt/kvm/kvm_main.c      |    7 ++++++-
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 9efdf5c..8c5c303 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -239,6 +239,8 @@ struct kvm_irq_routing_table {};
 struct kvm_memslots {
        u64 generation;
        struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM];
+       /* The mapping table from slot id to the index in memslots[]. */
+       int id_to_index[KVM_MEM_SLOTS_NUM];
 };

 struct kvm {
@@ -341,14 +343,13 @@ static inline struct kvm_memslots *kvm_memslots(struct 
kvm *kvm)
 static inline struct kvm_memory_slot *
 id_to_memslot(struct kvm_memslots *slots, int id)
 {
-       int i;
+       int index = slots->id_to_index[id];
+       struct kvm_memory_slot *slot;

-       for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
-               if (slots->memslots[i].id == id)
-                       return &slots->memslots[i];
+       slot = &slots->memslots[index];

-       WARN_ON(1);
-       return NULL;
+       WARN_ON(slot->id != id);
+       return slot;
 }

 #define HPA_MSB ((sizeof(hpa_t) * 8) - 1)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 6e8eb15..e289486 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -446,7 +446,7 @@ static void kvm_init_memslots_id(struct kvm *kvm)
        struct kvm_memslots *slots = kvm->memslots;

        for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
-               slots->memslots[i].id = i;
+               slots->id_to_index[i] = slots->memslots[i].id = i;
 }

 static struct kvm *kvm_create_vm(void)
@@ -674,8 +674,13 @@ static int cmp_memslot(const void *slot1, const void 
*slot2)
  */
 static void sort_memslots(struct kvm_memslots *slots)
 {
+       int i;
+
        sort(slots->memslots, KVM_MEM_SLOTS_NUM,
              sizeof(struct kvm_memory_slot), cmp_memslot, NULL);
+
+       for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
+               slots->id_to_index[slots->memslots[i].id] = i;
 }

 void update_memslots(struct kvm_memslots *slots, struct kvm_memory_slot *new)
-- 
1.7.7.3

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