netdev - [PATCH v2 net-next 3/3] net: use napi_skb

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Message-ID: <20251114121243.3519133-4-edumazet@google.com>
Date: Fri, 14 Nov 2025 12:12:43 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...gle.com>, 
	Jason Xing <kerneljasonxing@...il.com>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH v2 net-next 3/3] net: use napi_skb_cache even in process context

This is a followup of commit e20dfbad8aab ("net: fix napi_consume_skb()
with alien skbs").

Now the per-cpu napi_skb_cache is populated from TX completion path,
we can make use of this cache, especially for cpus not used
from a driver NAPI poll (primary user of napi_cache).

We can use the napi_skb_cache only if current context is not from hard irq.

With this patch, I consistently reach 130 Mpps on my UDP tx stress test
and reduce SLUB spinlock contention to smaller values.

Note there is still some SLUB contention for skb->head allocations.

I had to tune /sys/kernel/slab/skbuff_small_head/cpu_partial
and /sys/kernel/slab/skbuff_small_head/min_partial depending
on the platform taxonomy.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/skbuff.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index c6b065c0a2af265159ee6188469936767a295729..bda7e2196060f97c9fb7f8effd5276a7f5db3a74 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -662,8 +662,13 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
 	if (unlikely(node != NUMA_NO_NODE && node != numa_mem_id()))
 		goto fallback;

-	if (flags & SKB_ALLOC_NAPI)
+	if (flags & SKB_ALLOC_NAPI) {
 		skb = napi_skb_cache_get(true);
+	} else if (!in_hardirq() && !irqs_disabled()) {
+		local_bh_disable();
+		skb = napi_skb_cache_get(false);
+		local_bh_enable();
+	}

 	if (!skb) {
 fallback:
-- 
2.52.0.rc1.455.g30608eb744-goog