netdev - Re: stmmac ethernet in kernel 4.4: coalescing related pauses?

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Date:   Mon, 28 Nov 2016 07:31:43 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     lsanfil@...vell.com, pavel@....cz, peppe.cavallaro@...com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: stmmac ethernet in kernel 4.4: coalescing related pauses?

On Mon, 2016-11-28 at 09:54 -0500, David Miller wrote:
> From: Lino Sanfilippo <lsanfil@...vell.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));