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

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Date:   Mon, 28 Nov 2016 16:57:35 +0100
From:   Lino Sanfilippo <lsanfil@...vell.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>
CC:     <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 28.11.2016 16:31, Eric Dumazet wrote:
> 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));
>

I wonder if the best fix would be indeed to deactivate irq coalescing completely.
Does it make any sense at all to use it if a driver uses NAPI already?

Regards,
Lino