2014-11-14 12:12+0100, Paolo Bonzini:
> This completes the optimization from the previous patch, by
> removing the KVM_MEM_SLOTS_NUM-iteration loop from insert_memslot.
>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> virt/kvm/kvm_main.c | 39 +++++++++++++++++++--------------------
> 1 file changed, 19 insertions(+), 20 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index c0c2202e6c4f..c8ff99cc0ccb 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -677,31 +677,30 @@ static int kvm_create_dirty_bitmap(struct kvm_memory_slot *memslot)
> static void insert_memslot(struct kvm_memslots *slots,
> struct kvm_memory_slot *new)
> {
> - int i = slots->id_to_index[new->id];
> - struct kvm_memory_slot *old = id_to_memslot(slots, new->id);
> + int id = new->id;
> + int i = slots->id_to_index[id];
> struct kvm_memory_slot *mslots = slots->memslots;
>
> - if (new->npages == old->npages) {
> - *old = *new;
> - return;
> - }
> -
> - while (1) {
> - if (i < (KVM_MEM_SLOTS_NUM - 1) &&
> - new->npages < mslots[i + 1].npages) {
> - mslots[i] = mslots[i + 1];
> - i++;
> - } else if (i > 0 && new->npages > mslots[i - 1].npages) {
> - mslots[i] = mslots[i - 1];
> - i--;
> - } else {
> - mslots[i] = *new;
> - break;
> + WARN_ON(mslots[i].id != id);
> + if (new->npages != mslots[i].npages) {
> + while (1) {
> + if (i < (KVM_MEM_SLOTS_NUM - 1) &&
> + new->npages < mslots[i + 1].npages) {
(^^^^ whitespace error)
> + mslots[i] = mslots[i + 1];
> + slots->id_to_index[mslots[i].id] = i;
> + i++;
> + } else if (i > 0 &&
> + new->npages > mslots[i - 1].npages) {
> + mslots[i] = mslots[i - 1];
> + slots->id_to_index[mslots[i].id] = i;
> + i--;
> + } else
> + break;
We are replacing in a sorted array, so the the direction of our
traversal doesn't change, (and we could lose one tab level here,)
if (new->npages < mslots[i].npages) {
while (i < (KVM_MEM_SLOTS_NUM - 1) &&
new->npages < mslots[i + 1].npages) {
mslots[i] = mslots[i + 1];
slots->id_to_index[mslots[i].id] = i;
i++;
}
else if (new->npages > mslots[i].npages)
while (i > 0 &&
new->npages > mslots[i - 1].npages) {
mslots[i] = mslots[i - 1];
slots->id_to_index[mslots[i].id] = i;
i--;
}
(I guess you don't want me to abstract these two loops further :)
If the probability of slots with same npages was high, we could also
move just the last one from each group, but I think that the current
algorithm is already faster than we need.
(We'll have to change it into an interval tree, or something, if the
number of slots rises anyway.)
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