Linux Virtualization - Jan 2017 - [PATCH net 9/9] virtio-net: XDP support for small buffers

On 16-12-23 06:37 AM, Jason Wang wrote:
> Commit f600b6905015 ("virtio_net: Add XDP support") leaves the
case of
> small receive buffer untouched. This will confuse the user who want to
> set XDP but use small buffers. Other than forbid XDP in small buffer
> mode, let's make it work. XDP then can only work at skb->data since
> virtio-net create skbs during refill, this is sub optimal which could
> be optimized in the future.
> 
> Cc: John Fastabend <john.r.fastabend at intel.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
>  drivers/net/virtio_net.c | 112
++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 87 insertions(+), 25 deletions(-)
> 
Hi Jason,

I was doing some more testing on this what do you think about doing this
so that free_unused_bufs() handles the buffer free with dev_kfree_skb()
instead of put_page in small receive mode. Seems more correct to me.


diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 783e842..27ff76c 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1898,6 +1898,10 @@ static void free_receive_page_frags(struct virtnet_info
*vi)

 static bool is_xdp_queue(struct virtnet_info *vi, int q)
 {
+       /* For small receive mode always use kfree_skb variants */
+       if (!vi->mergeable_rx_bufs)
+               return false;
+
        if (q < (vi->curr_queue_pairs - vi->xdp_queue_pairs))
                return false;
        else if (q < vi->curr_queue_pairs)


patch is untested just spotted doing code review.

Thanks,
John

On 2017?01?03? 06:43, John Fastabend wrote:
> On 16-12-23 06:37 AM, Jason Wang wrote:
>> Commit f600b6905015 ("virtio_net: Add XDP support") leaves
the case of
>> small receive buffer untouched. This will confuse the user who want to
>> set XDP but use small buffers. Other than forbid XDP in small buffer
>> mode, let's make it work. XDP then can only work at skb->data
since
>> virtio-net create skbs during refill, this is sub optimal which could
>> be optimized in the future.
>>
>> Cc: John Fastabend <john.r.fastabend at intel.com>
>> Signed-off-by: Jason Wang <jasowang at redhat.com>
>> ---
>>   drivers/net/virtio_net.c | 112
++++++++++++++++++++++++++++++++++++-----------
>>   1 file changed, 87 insertions(+), 25 deletions(-)
>>
> Hi Jason,
>
> I was doing some more testing on this what do you think about doing this
> so that free_unused_bufs() handles the buffer free with dev_kfree_skb()
> instead of put_page in small receive mode. Seems more correct to me.
>
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 783e842..27ff76c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1898,6 +1898,10 @@ static void free_receive_page_frags(struct
virtnet_info *vi)
>
>   static bool is_xdp_queue(struct virtnet_info *vi, int q)
>   {
> +       /* For small receive mode always use kfree_skb variants */
> +       if (!vi->mergeable_rx_bufs)
> +               return false;
> +
>          if (q < (vi->curr_queue_pairs - vi->xdp_queue_pairs))
>                  return false;
>          else if (q < vi->curr_queue_pairs)
>
>
> patch is untested just spotted doing code review.
>
> Thanks,
> John
We probably need a better name for this function.

Acked-by: Jason Wang <jasowang at redhat.com>

On 17-01-02 10:16 PM, Jason Wang wrote:
> 
> 
> On 2017?01?03? 06:43, John Fastabend wrote:
>> On 16-12-23 06:37 AM, Jason Wang wrote:
>>> Commit f600b6905015 ("virtio_net: Add XDP support")
leaves the case of
>>> small receive buffer untouched. This will confuse the user who want
to
>>> set XDP but use small buffers. Other than forbid XDP in small
buffer
>>> mode, let's make it work. XDP then can only work at
skb->data since
>>> virtio-net create skbs during refill, this is sub optimal which
could
>>> be optimized in the future.
>>>
>>> Cc: John Fastabend <john.r.fastabend at intel.com>
>>> Signed-off-by: Jason Wang <jasowang at redhat.com>
>>> ---
>>>   drivers/net/virtio_net.c | 112
++++++++++++++++++++++++++++++++++++-----------
>>>   1 file changed, 87 insertions(+), 25 deletions(-)
>>>
>> Hi Jason,
>>
>> I was doing some more testing on this what do you think about doing
this
>> so that free_unused_bufs() handles the buffer free with dev_kfree_skb()
>> instead of put_page in small receive mode. Seems more correct to me.
>>
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 783e842..27ff76c 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -1898,6 +1898,10 @@ static void free_receive_page_frags(struct
virtnet_info
>> *vi)
>>
>>   static bool is_xdp_queue(struct virtnet_info *vi, int q)
>>   {
>> +       /* For small receive mode always use kfree_skb variants */
>> +       if (!vi->mergeable_rx_bufs)
>> +               return false;
>> +
>>          if (q < (vi->curr_queue_pairs - vi->xdp_queue_pairs))
>>                  return false;
>>          else if (q < vi->curr_queue_pairs)
>>
>>
>> patch is untested just spotted doing code review.
>>
>> Thanks,
>> John
> 
> We probably need a better name for this function.
> 
> Acked-by: Jason Wang <jasowang at redhat.com>
> 
How about is_xdp_raw_buffer_queue()?

I'll submit a proper patch today.