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

On 2017年08月15日 00:01, Michael S. Tsirkin wrote:

On Sat, Aug 12, 2017 at 10:48:49AM +0800, Jason Wang wrote:

quoted

On 2017年08月12日 07:12, Jakub Kicinski wrote:

quoted

On Fri, 11 Aug 2017 19:41:18 +0800, Jason Wang wrote:

quoted

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 <redacted>

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

What did you test btw?

Pktgen

  The biggest issue would be with something like
UDP with short packets.

Note that we do this only when sndbuf is INT_MAX. So this is probably not an issue. The only thing matter is more stress to page allocator, but according to the result of pktgen it was very small that could be ignored.

Thanks