Linux Virtualization - Jan 2014 - [PATCH net-next RFC] virtio-net: drop rq->max and rq->num

Rusty Russell <rusty at rustcorp.com.au> writes:
> Jason Wang <jasowang at redhat.com> writes:
>> It looks like there's no need for those two fields:
>>
>> - Unless there's a failure for the first refill try, rq->max
should be always
>>   equal to the vring size.
>> - rq->num is only used to determine the condition that we need to do
the refill,
>>   we could check vq->num_free instead.
>> - rq->num was required to be increased or decreased explicitly after
each
>>   get/put which results a bad API.
>>
>> So this patch removes them both to make the code simpler.
>
> Nice.  These fields date from when the vq struct was opaque.
>
> Applied,
> Rusty.
Oops, this doesn't require any core virtio changes, so it's for DaveM:

Acked-by: Rusty Russell <rusty at rustcorp.com.au>

Thanks,
Rusty.
>> Cc: Rusty Russell <rusty at rustcorp.com.au>
>> Cc: Michael S. Tsirkin <mst at redhat.com>
>> Signed-off-by: Jason Wang <jasowang at redhat.com>
>> ---
>>  drivers/net/virtio_net.c | 16 +++-------------
>>  1 file changed, 3 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index c51a988..4e1bce3 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -72,9 +72,6 @@ struct receive_queue {
>>  
>>  	struct napi_struct napi;
>>  
>> -	/* Number of input buffers, and max we've ever had. */
>> -	unsigned int num, max;
>> -
>>  	/* Chain pages by the private ptr. */
>>  	struct page *pages;
>>  
>> @@ -360,7 +357,6 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>>  		}
>>  
>>  		page = virt_to_head_page(buf);
>> -		--rq->num;
>>  
>>  		num_skb_frags = skb_shinfo(curr_skb)->nr_frags;
>>  		if (unlikely(num_skb_frags == MAX_SKB_FRAGS)) {
>> @@ -406,7 +402,6 @@ err_skb:
>>  		}
>>  		page = virt_to_head_page(buf);
>>  		put_page(page);
>> -		--rq->num;
>>  	}
>>  err_buf:
>>  	dev->stats.rx_dropped++;
>> @@ -628,10 +623,7 @@ static bool try_fill_recv(struct receive_queue
*rq, gfp_t gfp)
>>  		oom = err == -ENOMEM;
>>  		if (err)
>>  			break;
>> -		++rq->num;
>>  	} while (rq->vq->num_free);
>> -	if (unlikely(rq->num > rq->max))
>> -		rq->max = rq->num;
>>  	if (unlikely(!virtqueue_kick(rq->vq)))
>>  		return false;
>>  	return !oom;
>> @@ -699,11 +691,10 @@ again:
>>  	while (received < budget &&
>>  	       (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
>>  		receive_buf(rq, buf, len);
>> -		--rq->num;
>>  		received++;
>>  	}
>>  
>> -	if (rq->num < rq->max / 2) {
>> +	if (rq->vq->num_free > virtqueue_get_vring_size(rq->vq) /
2) {
>>  		if (!try_fill_recv(rq, GFP_ATOMIC))
>>  			schedule_delayed_work(&vi->refill, 0);
>>  	}
>> @@ -1398,9 +1389,7 @@ static void free_unused_bufs(struct virtnet_info
*vi)
>>  				give_pages(&vi->rq[i], buf);
>>  			else
>>  				dev_kfree_skb(buf);
>> -			--vi->rq[i].num;
>>  		}
>> -		BUG_ON(vi->rq[i].num != 0);
>>  	}
>>  }
>>  
>> @@ -1671,7 +1660,8 @@ static int virtnet_probe(struct virtio_device
*vdev)
>>  		try_fill_recv(&vi->rq[i], GFP_KERNEL);
>>  
>>  		/* If we didn't even get one input buffer, we're useless. */
>> -		if (vi->rq[i].num == 0) {
>> +		if (vi->rq[i].vq->num_free =>> +		   
virtqueue_get_vring_size(vi->rq[i].vq)) {
>>  			free_unused_bufs(vi);
>>  			err = -ENOMEM;
>>  			goto free_recv_bufs;
>> -- 
>> 1.8.3.2
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From: Rusty Russell <rusty at rustcorp.com.au>
Date: Thu, 16 Jan 2014 10:25:26 +1030
> Rusty Russell <rusty at rustcorp.com.au> writes:
>> Jason Wang <jasowang at redhat.com> writes:
>>> It looks like there's no need for those two fields:
>>>
>>> - Unless there's a failure for the first refill try, rq->max
should be always
>>>   equal to the vring size.
>>> - rq->num is only used to determine the condition that we need
to do the refill,
>>>   we could check vq->num_free instead.
>>> - rq->num was required to be increased or decreased explicitly
after each
>>>   get/put which results a bad API.
>>>
>>> So this patch removes them both to make the code simpler.
>>
>> Nice.  These fields date from when the vq struct was opaque.
>>
>> Applied,
>> Rusty.
> 
> Oops, this doesn't require any core virtio changes, so it's for
DaveM:
> 
> Acked-by: Rusty Russell <rusty at rustcorp.com.au>
Jason please repost this with Rusty's ACK, thanks.

On 01/16/2014 08:46 AM, David Miller wrote:
> From: Rusty Russell<rusty at rustcorp.com.au>
> Date: Thu, 16 Jan 2014 10:25:26 +1030
>
>> Rusty Russell<rusty at rustcorp.com.au>  writes:
>>> Jason Wang<jasowang at redhat.com>  writes:
>>>> It looks like there's no need for those two fields:
>>>>
>>>> - Unless there's a failure for the first refill try,
rq->max should be always
>>>>    equal to the vring size.
>>>> - rq->num is only used to determine the condition that we
need to do the refill,
>>>>    we could check vq->num_free instead.
>>>> - rq->num was required to be increased or decreased
explicitly after each
>>>>    get/put which results a bad API.
>>>>
>>>> So this patch removes them both to make the code simpler.
>>> Nice.  These fields date from when the vq struct was opaque.
>>>
>>> Applied,
>>> Rusty.
>> Oops, this doesn't require any core virtio changes, so it's for
DaveM:
>>
>> Acked-by: Rusty Russell<rusty at rustcorp.com.au>
> Jason please repost this with Rusty's ACK, thanks.
Sure, will repost.