netdev - [PATCH net-next] Revert "net: snmp: add statistics for tcp small queue check"

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Message-Id: <20211201033246.2826224-1-eric.dumazet@gmail.com>
Date:   Tue, 30 Nov 2021 19:32:46 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Menglong Dong <imagedong@...cent.com>
Subject: [PATCH net-next] Revert "net: snmp: add statistics for tcp small queue check"

From: Eric Dumazet <edumazet@...gle.com>

This reverts commit aeeecb889165617a841e939117f9a8095d0e7d80.

The new SNMP variable (TCPSmallQueueFailure) can be incremented
for good reasons, even on a 100Gbit single TCP_STREAM flow.

If we really wanted to ease driver debugging [1], this would
require something more sophisticated.

[1] Usually, if a driver is delaying TX completions too much,
this can lead to stalls in TCP output. Various work arounds
have been used in the past, like skb_orphan() in ndo_start_xmit().

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Menglong Dong <imagedong@...cent.com>
---
 include/uapi/linux/snmp.h | 1 -
 net/ipv4/proc.c           | 1 -
 net/ipv4/tcp_output.c     | 5 +----
 3 files changed, 1 insertion(+), 6 deletions(-)

diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
index e32ec6932e8200fbc9e1f27d00bd43e7b34633d4..904909d020e2c8974128392370540c0ba3af4e15 100644
--- a/include/uapi/linux/snmp.h
+++ b/include/uapi/linux/snmp.h
@@ -292,7 +292,6 @@ enum
 	LINUX_MIB_TCPDSACKIGNOREDDUBIOUS,	/* TCPDSACKIgnoredDubious */
 	LINUX_MIB_TCPMIGRATEREQSUCCESS,		/* TCPMigrateReqSuccess */
 	LINUX_MIB_TCPMIGRATEREQFAILURE,		/* TCPMigrateReqFailure */
-	LINUX_MIB_TCPSMALLQUEUEFAILURE,		/* TCPSmallQueueFailure */
 	__LINUX_MIB_MAX
 };
 
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 43b7a77cd6b4588cc10150613cf05154640d679f..f30273afb5399ddf0122e46e36da2ddae720a1c3 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -297,7 +297,6 @@ static const struct snmp_mib snmp4_net_list[] = {
 	SNMP_MIB_ITEM("TCPDSACKIgnoredDubious", LINUX_MIB_TCPDSACKIGNOREDDUBIOUS),
 	SNMP_MIB_ITEM("TCPMigrateReqSuccess", LINUX_MIB_TCPMIGRATEREQSUCCESS),
 	SNMP_MIB_ITEM("TCPMigrateReqFailure", LINUX_MIB_TCPMIGRATEREQFAILURE),
-	SNMP_MIB_ITEM("TCPSmallQueueFailure", LINUX_MIB_TCPSMALLQUEUEFAILURE),
 	SNMP_MIB_SENTINEL
 };
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c4ab6c8f0c77d32e1c4e7e558a6a0f0aa17a5986..5079832af5c1090917a8fd5dfb1a3025e2d85ae0 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2524,11 +2524,8 @@ static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb,
 		 * test again the condition.
 		 */
 		smp_mb__after_atomic();
-		if (refcount_read(&sk->sk_wmem_alloc) > limit) {
-			NET_INC_STATS(sock_net(sk),
-				      LINUX_MIB_TCPSMALLQUEUEFAILURE);
+		if (refcount_read(&sk->sk_wmem_alloc) > limit)
 			return true;
-		}
 	}
 	return false;
 }
-- 
2.34.0.rc2.393.gf8c9666880-goog