[PATCH net-next] tcp: try to defer / return acked skbs to originating CPU

[Jakub Kicinski <kuba@kernel.org>]

Running a memcache-like workload under production(ish) load
on a 300 thread AMD machine we see ~3% of CPU time spent
in kmem_cache_free() via tcp_ack(), freeing skbs from rtx queue.
This workloads pins workers away from softirq CPU so
the Tx skbs are pretty much always allocated on a different
CPU than where the ACKs arrive. Try to use the defer skb free
queue to return the skbs back to where they came from.
This results in a ~4% performance improvement for the workload.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 include/net/tcp.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index ef0fee58fde8..e290651da508 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -332,7 +332,7 @@ static inline void tcp_wmem_free_skb(struct sock *sk, struct sk_buff *skb)
 		sk_mem_uncharge(sk, skb->truesize);
 	else
 		sk_mem_uncharge(sk, SKB_TRUESIZE(skb_end_offset(skb)));
-	__kfree_skb(skb);
+	skb_attempt_defer_free(skb);
 }
 
 void sk_forced_mem_schedule(struct sock *sk, int size);
-- 
2.52.0