netdev - [PATCH v1 2/2] tcp: Ignore OOO handling for TCP ACKs

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Message-Id: <20221020182242.503107-3-kamaljit.singh1@wdc.com>
Date:   Thu, 20 Oct 2022 11:22:42 -0700
From:   Kamaljit Singh <kamaljit.singh1@....com>
To:     edumazet@...gle.com, davem@...emloft.net, yoshfuji@...ux-ipv6.org,
        dsahern@...nel.org, kuba@...nel.org, pabeni@...hat.com
Cc:     netdev@...r.kernel.org, Niklas.Cassel@....com,
        Damien.LeMoal@....com, kamaljit.singh1@....com
Subject: [PATCH v1 2/2] tcp: Ignore OOO handling for TCP ACKs

Even with the TCP window fix to tcp_acceptable_seq(), occasional
out-of-order host ACKs were still seen under heavy write workloads thus
Impacting performance.  By removing the OoO optionality for ACKs in
__tcp_transmit_skb() that issue seems to be fixed as well.

Signed-off-by: Kamaljit Singh <kamaljit.singh1@....com>
---
 net/ipv4/tcp_output.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 322e061edb72..1cd77493f32c 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1307,7 +1307,10 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
 	 * TODO: Ideally, in-flight pure ACK packets should not matter here.
 	 * One way to get this would be to set skb->truesize = 2 on them.
 	 */
-	skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
+	if (likely(tcb->tcp_flags & TCPHDR_ACK))
+		skb->ooo_okay = 0;
+	else
+		skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
 
 	/* If we had to use memory reserve to allocate this skb,
 	 * this might cause drops if packet is looped back :
-- 
2.25.1