[RFC PATCH net-next v3 2/2] net: veth: Optimizing skb reuse in NAPI Context

[Liang Chen <liangchen.linux@gmail.com>]

In cases where the skb is reallocated by veth_convert_skb_to_xdp_buff,
we leverage the NAPI version of the "head stolen" function to enable
fast skb reuse. The following test results evaluate the performance
improvement resulting from reusing skb in the NAPI context with
pktgen-generated traffic.

Test environment setup:
ns1                 ns2
veth0   <-peer->    veth1
veth2   <-peer->    veth3

Test Results:
pktgen -> veth1 -> veth0(XDP_TX) -> veth1(XDP_DROP)
    without reusing skb: 2,033,439
    reusing skb: 2,167,749
    improvement: ~6%

pktgen -> veth1 -> veth0(XDP_TX) -> veth1(XDP_PASS)
    without reusing skb: 1,585,462
    reusing skb: 1,650,572
    improvement: ~4%

pktgen -> veth1 -> veth0(XDP_REDIRECT) -> veth2 -> veth3(XDP_DROP)
    without reusing skb: 1,787,342
    reusing skb: 1,848,516
    improvement: ~3%

pktgen -> veth1 -> veth0(XDP_REDIRECT) -> veth2 -> veth3(XDP_PASS)
    without reusing skb: 1,391,587
    reusing skb: 1,439,866
    improvement: ~3%

pktgen -> veth1 -> veth0(AF_XDP) -> user space(DROP)
    without reusing skb: 1,811,844
    with reusing skb: 1,861,027
    improvement: ~3%

Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
---
 drivers/net/veth.c | 5 ++++-
 net/core/skbuff.c  | 1 +
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 7234eb0297dd..4e1ee110ab84 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -838,9 +838,12 @@ static void __skb2xdp_steal_data(struct sk_buff *skb,
 	if (local_pp_alloc) {
 		/* This is the most common case where the skb was reallocated locally in
 		 * veth_convert_skb_to_xdp_buff, and it's safe to use the xdp_mem_pp model.
+		 * Since the skb is "reallocated" in the NAPI context of veth, it is possible
+		 * to use the NAPI version of the "head stolen" function to optimize the
+		 * reuse of skb as well.
 		 */
 		xdp->rxq->mem = rq->xdp_mem_pp;
-		kfree_skb_partial(skb, true);
+		napi_skb_free_stolen_head(skb);
 	} else if (!skb->pp_recycle) {
 		/* We can safely use kfree_skb_partial here because this cannot be an fclone
 		 * skb. Fclone skbs are allocated via __alloc_skb, with their head buffer
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index a298992060e6..954ba1b94840 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1284,6 +1284,7 @@ void napi_skb_free_stolen_head(struct sk_buff *skb)
 	}
 	napi_skb_cache_put(skb);
 }
+EXPORT_SYMBOL(napi_skb_free_stolen_head);
 
 void napi_consume_skb(struct sk_buff *skb, int budget)
 {
-- 
2.40.1