Re: [PATCH net-next V2 3/3] tap: XDP support

[Jason Wang <jasowang@redhat.com>]

On 2017年08月12日 07:12, Jakub Kicinski wrote:
> On Fri, 11 Aug 2017 19:41:18 +0800, Jason Wang wrote:
>> This patch tries to implement XDP for tun. The implementation was
>> split into two parts:
>>
>> - fast path: small and no gso packet. We try to do XDP at page level
>>    before build_skb(). For XDP_TX, since creating/destroying queues
>>    were completely under control of userspace, it was implemented
>>    through generic XDP helper after skb has been built. This could be
>>    optimized in the future.
>> - slow path: big or gso packet. We try to do it after skb was created
>>    through generic XDP helpers.
>>
>> Test were done through pktgen with small packets.
>>
>> xdp1 test shows ~41.1% improvement:
>>
>> Before: ~1.7Mpps
>> After:  ~2.3Mpps
>>
>> xdp_redirect to ixgbe shows ~60% improvement:
>>
>> Before: ~0.8Mpps
>> After:  ~1.38Mpps
>>
>> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
> Looks OK to me now :)
>
> Out of curiosity, you say the build_skb() is for "small packets", and it
> seems you are always reserving the 256B regardless of XDP being
> installed.  Does this have no performance impact on non-XDP case?

Have a test, only less than 1% were noticed which I think could be ignored.

Thanks