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

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@xxxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
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.