linux-kernel - Re: [PATCH net-next RFC 2/5] vhost: introduce helper to prefetch desc index

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Date:   Mon, 25 Sep 2017 10:04:13 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Stefan Hajnoczi <stefanha@...il.com>
Cc:     mst@...hat.com, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH net-next RFC 2/5] vhost: introduce helper to prefetch desc
 index



On 2017年09月22日 17:02, Stefan Hajnoczi wrote:
> On Fri, Sep 22, 2017 at 04:02:32PM +0800, Jason Wang wrote:
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index f87ec75..8424166d 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -2437,6 +2437,61 @@ struct vhost_msg_node *vhost_dequeue_msg(struct vhost_dev *dev,
>>   }
>>   EXPORT_SYMBOL_GPL(vhost_dequeue_msg);
>>   
>> +int vhost_prefetch_desc_indices(struct vhost_virtqueue *vq,
>> +				struct vring_used_elem *heads,
>> +				u16 num, bool used_update)
> Missing doc comment.

Will fix this.

>
>> +{
>> +	int ret, ret2;
>> +	u16 last_avail_idx, last_used_idx, total, copied;
>> +	__virtio16 avail_idx;
>> +	struct vring_used_elem __user *used;
>> +	int i;
> The following variable names are a little confusing:
>
> last_avail_idx vs vq->last_avail_idx.  last_avail_idx is a wrapped
> avail->ring[] index, vq->last_avail_idx is a free-running counter.  The
> same for last_used_idx vs vq->last_used_idx.
>
> num argument vs vq->num.  The argument could be called nheads instead to
> make it clear that this is heads[] and not the virtqueue size.
>
> Not a bug but it took me a while to figure out what was going on.

I admit the name is confusing. Let me try better ones in V2.

Thanks