[PATCH v3 net-next] net: advance skb_defer_disable_key check in napi_consume_skb

[Jason Xing <kerneljasonxing@gmail.com>]

From: Jason Xing <kernelxing@tencent.com>

When net.core.skb_defer_max is adjusted to zero, napi_consume_skb
shouldn't go into deeper in skb_attempt_defer_free because that function
adds a pair of local_bh_enable/disable() which can be found in
kfree_skb_napi_cache(). Advancing the check of the static key saves more
cycles and benefits the single flow/few flows workloads.

Signed-off-by: Jason Xing <kernelxing@tencent.com>
---
v3
Link: https://lore.kernel.org/all/20260327153347.98647-1-kerneljasonxing@gmail.com/
1. use a simpler approach to avoid adding a new sysctl.

V2
Link: https://lore.kernel.org/all/20260326144249.97213-1-kerneljasonxing@gmail.com/
1. reuse proc_do_static_key() (Eric)
2. add doc (Stan)
---
 net/core/skbuff.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 3d6978dd0aa8..c1562ba6903e 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1519,7 +1519,8 @@ void napi_consume_skb(struct sk_buff *skb, int budget)
 
 	DEBUG_NET_WARN_ON_ONCE(!in_softirq());
 
-	if (skb->alloc_cpu != smp_processor_id() && !skb_shared(skb)) {
+	if (!static_branch_unlikely(&skb_defer_disable_key) &&
+	    skb->alloc_cpu != smp_processor_id() && !skb_shared(skb)) {
 		skb_release_head_state(skb);
 		return skb_attempt_defer_free(skb);
 	}
-- 
2.41.3