netdev - [PATCH net] af_packet: do not call packet_read_pending() from tpacket_destruct

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Message-ID: <20240515163358.4105915-1-edumazet@google.com>
Date: Wed, 15 May 2024 16:33:58 +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: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>, Neil Horman <nhorman@...driver.com>, 
	Daniel Borkmann <daniel@...earbox.net>, Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: [PATCH net] af_packet: do not call packet_read_pending() from tpacket_destruct_skb()

trafgen performance considerably sank on hosts with many cores
after the blamed commit.

packet_read_pending() is very expensive, and calling it
in af_packet fast path defeats Daniel intent in commit
b013840810c2 ("packet: use percpu mmap tx frame pending refcount")

tpacket_destruct_skb() makes room for one packet, we can immediately
wakeup a producer, no need to completely drain the tx ring.

Fixes: 89ed5b519004 ("af_packet: Block execution of tasks waiting for transmit to complete in AF_PACKET")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Neil Horman <nhorman@...driver.com>
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>
---
 net/packet/af_packet.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 8c6d3fbb4ed87f17c2e365810106a05fe9b8ff0c..ea3ebc160e25cc661901717a755f47db927c304d 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2522,8 +2522,7 @@ static void tpacket_destruct_skb(struct sk_buff *skb)
 		ts = __packet_set_timestamp(po, ph, skb);
 		__packet_set_status(po, ph, TP_STATUS_AVAILABLE | ts);
 
-		if (!packet_read_pending(&po->tx_ring))
-			complete(&po->skb_completion);
+		complete(&po->skb_completion);
 	}
 
 	sock_wfree(skb);
-- 
2.45.0.rc1.225.g2a3ae87e7f-goog