af_packet: do not call packet_read_pending() from tpacket_destruct_skb()

JIRA: https://issues.redhat.com/browse/RHEL-78307

commit 581073f
Author: Eric Dumazet <edumazet@google.com>
Date:   Wed May 15 16:33:58 2024 +0000

    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
    b013840 ("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: 89ed5b5 ("af_packet: Block execution of tasks waiting for transmit to complete in AF_PACKET")
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Cc: Neil Horman <nhorman@tuxdriver.com>
    Cc: Daniel Borkmann <daniel@iogearbox.net>
    Reviewed-by: Willem de Bruijn <willemb@google.com>
    Link: https://lore.kernel.org/r/20240515163358.4105915-1-edumazet@google.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

net/packet/af_packet.c

@@ -2489,8 +2489,7 @@ 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);