netdev - Re: [net-next PATCH] mvneta: add XDP ethtool errors stats for TX to driver

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Date:   Mon, 02 Mar 2020 11:29:58 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     brouer@...hat.com
Cc:     netdev@...r.kernel.org, ilias.apalodimas@...aro.org,
        lorenzo@...nel.org, dsahern@...il.com, toke@...e.dk,
        saeedm@...lanox.com, tariqt@...lanox.com, kuba@...nel.org,
        andrew@...n.ch, thomas.petazzoni@...tlin.com
Subject: Re: [net-next PATCH] mvneta: add XDP ethtool errors stats for TX
 to driver

From: Jesper Dangaard Brouer <brouer@...hat.com>
Date: Mon, 02 Mar 2020 14:46:28 +0100

> Adding ethtool stats for when XDP transmitted packets overrun the TX
> queue. This is recorded separately for XDP_TX and ndo_xdp_xmit. This
> is an important aid for troubleshooting XDP based setups.
> 
> It is currently a known weakness and property of XDP that there isn't
> any push-back or congestion feedback when transmitting frames via XDP.
> It's easy to realise when redirecting from a higher speed link into a
> slower speed link, or simply two ingress links into a single egress.
> The situation can also happen when Ethernet flow control is active.
> 
> For testing the patch and provoking the situation to occur on my
> Espressobin board, I configured the TX-queue to be smaller (434) than
> RX-queue (512) and overload network with large MTU size frames (as a
> larger frame takes longer to transmit).
> 
> Hopefully the upcoming XDP TX hook can be extended to provide insight
> into these TX queue overflows, to allow programmable adaptation
> strategies.
> 
> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>

Applied, thanks Jesper.