netdev - Re: [PATCH net-next 3/5] virtio-net: switch to use new ctx API for small buffer

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Date:   Wed, 19 Jul 2017 10:30:23 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 3/5] virtio-net: switch to use new ctx API for
 small buffer



On 2017年07月19日 03:20, Michael S. Tsirkin wrote:
> what's needed is ability to store the headroom there.
>
> virtio-net: switch to use ctx API for small buffers
>
> Use ctx API to store headroom for small buffers.
> Following patches will retrieve this info and use it for XDP.
>
> On Mon, Jul 17, 2017 at 08:43:59PM +0800, Jason Wang wrote:
>> Switch to use ctx API for small buffer, this is need for avoiding
>> reset on XDP.
>>
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>> ---
>>   drivers/net/virtio_net.c | 12 +++++++-----
>>   1 file changed, 7 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 8fae9a8..e31b5b2 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -410,7 +410,8 @@ static unsigned int virtnet_get_headroom(struct virtnet_info *vi)
>>   static struct sk_buff *receive_small(struct net_device *dev,
>>   				     struct virtnet_info *vi,
>>   				     struct receive_queue *rq,
>> -				     void *buf, unsigned int len)
>> +				     void *buf, void *ctx,
>> +				     unsigned int len)
>>   {
>>   	struct sk_buff *skb;
>>   	struct bpf_prog *xdp_prog;
>> @@ -773,7 +774,7 @@ static int receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
>>   	else if (vi->big_packets)
>>   		skb = receive_big(dev, vi, rq, buf, len);
>>   	else
>> -		skb = receive_small(dev, vi, rq, buf, len);
>> +		skb = receive_small(dev, vi, rq, buf, ctx, len);
>>   
>>   	if (unlikely(!skb))
>>   		return 0;
>> @@ -812,6 +813,7 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
> Let's document that ctx API is used a bit differently here:
>
> /* Unlike mergeable buffers, all buffers are allocated to the same size,
>   * except for the headroom. For this reason we do not need to use
>   * mergeable_len_to_ctx here - it is enough to store the headroom as the
>   * context ignoring the truesize.
>   */

Ok.

Thanks

> as an alternative, reuse the same format as mergeable buffers.
>
>>   	struct page_frag *alloc_frag = &rq->alloc_frag;
>>   	char *buf;
>>   	unsigned int xdp_headroom = virtnet_get_headroom(vi);
>> +	void *ctx = (void *)(unsigned long)xdp_headroom;
>>   	int len = vi->hdr_len + VIRTNET_RX_PAD + GOOD_PACKET_LEN + xdp_headroom;
>>   	int err;
>>   
>> @@ -825,7 +827,7 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
>>   	alloc_frag->offset += len;
>>   	sg_init_one(rq->sg, buf + VIRTNET_RX_PAD + xdp_headroom,
>>   		    vi->hdr_len + GOOD_PACKET_LEN);
>> -	err = virtqueue_add_inbuf(rq->vq, rq->sg, 1, buf, gfp);
>> +	err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
>>   	if (err < 0)
>>   		put_page(virt_to_head_page(buf));
>>   
>> @@ -1034,7 +1036,7 @@ static int virtnet_receive(struct receive_queue *rq, int budget)
>>   	void *buf;
>>   	struct virtnet_stats *stats = this_cpu_ptr(vi->stats);
>>   
>> -	if (vi->mergeable_rx_bufs) {
>> +	if (!vi->big_packets || vi->mergeable_rx_bufs) {
>>   		void *ctx;
>>   
>>   		while (received < budget &&
>> @@ -2198,7 +2200,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
>>   	names = kmalloc(total_vqs * sizeof(*names), GFP_KERNEL);
>>   	if (!names)
>>   		goto err_names;
>> -	if (vi->mergeable_rx_bufs) {
>> +	if (!vi->big_packets || vi->mergeable_rx_bufs) {
>>   		ctx = kzalloc(total_vqs * sizeof(*ctx), GFP_KERNEL);
>>   		if (!ctx)
>>   			goto err_ctx;
>> -- 
>> 2.7.4