netdev - [PATCH net-next v2] net: cache for same cpu skb_attempt_defer

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Date: Mon, 18 Mar 2024 00:44:22 +0000
From: Pavel Begunkov <asml.silence@...il.com>
To: netdev@...r.kernel.org,
	edumazet@...gle.com,
	davem@...emloft.net,
	dsahern@...nel.org,
	pabeni@...hat.com,
	kuba@...nel.org
Cc: Pavel Begunkov <asml.silence@...il.com>
Subject: [PATCH net-next v2] net: cache for same cpu skb_attempt_defer_free

Optimise skb_attempt_defer_free() when run by the same CPU the skb was
allocated on. Instead of __kfree_skb() -> kmem_cache_free() we can
disable softirqs and put the buffer into cpu local caches.

CPU bound TCP ping pong style benchmarking (i.e. netbench) showed a 1%
throughput increase (392.2 -> 396.4 Krps). Cross checking with profiles,
the total CPU share of skb_attempt_defer_free() dropped by 0.6%. Note,
I'd expect the win doubled with rx only benchmarks, as the optimisation
is for the receive path, but the test spends >55% of CPU doing writes.

Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---

v2: pass @napi_safe=true by using __napi_kfree_skb()

 net/core/skbuff.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index b99127712e67..35d37ae70a3d 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -6995,6 +6995,19 @@ void __skb_ext_put(struct skb_ext *ext)
 EXPORT_SYMBOL(__skb_ext_put);
 #endif /* CONFIG_SKB_EXTENSIONS */
 
+static void kfree_skb_napi_cache(struct sk_buff *skb)
+{
+	/* if SKB is a clone, don't handle this case */
+	if (skb->fclone != SKB_FCLONE_UNAVAILABLE) {
+		__kfree_skb(skb);
+		return;
+	}
+
+	local_bh_disable();
+	__napi_kfree_skb(skb, SKB_DROP_REASON_NOT_SPECIFIED);
+	local_bh_enable();
+}
+
 /**
  * skb_attempt_defer_free - queue skb for remote freeing
  * @skb: buffer
@@ -7013,7 +7026,7 @@ void skb_attempt_defer_free(struct sk_buff *skb)
 	if (WARN_ON_ONCE(cpu >= nr_cpu_ids) ||
 	    !cpu_online(cpu) ||
 	    cpu == raw_smp_processor_id()) {
-nodefer:	__kfree_skb(skb);
+nodefer:	kfree_skb_napi_cache(skb);
 		return;
 	}
 
-- 
2.44.0