linux-kernel - Re: [PATCH v2 6/6] KVM: introduce a table to map slot id to index in memslots arry

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Date:	Fri, 18 Nov 2011 11:45:36 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 6/6] KVM: introduce a table to map slot id to index
 in memslots arry

On Fri, 2011-11-18 at 17:20 +0800, Xiao Guangrong wrote:
> The operation of getting dirty log is frequency 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 <xiaoguangrong@...ux.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 83b396a..fbf66eb 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -238,6 +238,8 @@ 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 {
> @@ -340,14 +342,13 @@ 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;
>  }

If we didn't find the right memslot we shouldn't be returning a wrong
one, we should be failing.

-- 

Sasha.

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