From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: stmmac ethernet in kernel 4.4: coalescing related pauses?
Date: Mon, 28 Nov 2016 07:31:43 -0800
Message-ID: <1480347103.18162.58.camel@edumazet-glaptop3.roam.corp.google.com>
References: <20161123105125.GA26394@amd>
         <f14255ee-7fa8-afef-23ec-fc4f9a74eec8@marvell.com>
         <20161128.095431.856183735501262965.davem@davemloft.net>
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Cc: lsanfil@marvell.com, pavel@ucw.cz, peppe.cavallaro@st.com,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
To: David Miller <davem@davemloft.net>
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On Mon, 2016-11-28 at 09:54 -0500, David Miller wrote:
> From: Lino Sanfilippo <lsanfil@marvell.com>
> Date: Mon, 28 Nov 2016 14:07:51 +0100
> 
> > Calling skb_orphan() in the xmit handler made this issue disappear.
> 
> This is not the way to handle this problem.
> 
> The solution is to free the SKBs in a timely manner after the
> chip has transmitted the frame.

Note that the 'pauses' described by Pavel are also caused by a too small
SO_SNDBUF value on the UDP socket.

An immediate fix, with no kernel change is to increase it.

echo 1000000 >/proc/sys/net/core/wmem_default

or

val = 1000000;
setsockopt(fd, SOL_SOCKET, SO_SNDBUF, &val, sizeof(val));