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From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH] tcp: ensure non-empty connection request queue
Date: Wed, 04 May 2016 11:18:25 -0700
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Cc: Peter Wu <peter@lekensteyn.nl>,
	"David S . Miller" <davem@davemloft.net>, netdev@vger.kernel.org,
	Eric Dumazet <edumazet@google.com>,
	Kui Zhang <kuizhang@gmail.com>
To: Rick Jones <rick.jones2@hpe.com>
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On Wed, 2016-05-04 at 11:05 -0700, Rick Jones wrote:

> Assuming Peter's assertion about just drops when syncookies are not 
> enabled is accurate, should there be some one-time message in that case too?

We have plenty of drop points in the kernel without a message in syslog,
but proper SNMP counter updates.

Look at my recent commit 
9caad864151e525 ("tcp: increment sk_drops for listeners")

"ss -tm state listening" will show you the drop count per listener.