netdev - Re: [PATCH net 0/1] Prevent DSA tags from breaking COE

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Date: Tue, 19 Dec 2023 14:30:16 +0200
From: Vladimir Oltean <olteanv@...il.com>
To: Romain Gantois <romain.gantois@...tlin.com>
Cc: Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Jose Abreu <joabreu@...opsys.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Miquel Raynal <miquel.raynal@...tlin.com>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	Sylvain Girard <sylvain.girard@...com>,
	Pascal EBERHARD <pascal.eberhard@...com>,
	Richard Tresidder <rtresidd@...ctromag.com.au>,
	netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net 0/1] Prevent DSA tags from breaking COE

On Mon, Dec 18, 2023 at 05:23:22PM +0100, Romain Gantois wrote:
> I've run some iperf3 tests and the TX hotpath performance doesn't seem
> to be degraded by the field added to dma_features.

I don't know what CPU cores you are using, but if the iperf3 performance
was line rate at gigabit before and is line rate at gigabit now, you
haven't effectively measured the impact of the change (and "doesn't seem
to be degraded" is a false conclusion). You need something more CPU
intensive to see the difference, like IP forwarding of 64 byte packets.

A very simplistic way to set up IP forwarding between 2 DSA user ports
is to do this on the router board (DUT):

echo 1 > /proc/sys/net/ipv4/ip_forward
ip link set swp0 up && ip addr add 192.168.100.2/24 dev swp0
ip link set swp1 up && ip addr add 192.168.101.2/24 dev swp1

and this on the system with 2 endpoints:

ip netns add ns0
ip link set $ETH1 netns ns0
ip link set $ETH0 up && ip addr add 192.168.100.1/24 dev $ETH0
ip -n ns0 link set $ETH1 up && ip -n ns0 addr add 192.168.101.1/24 dev $ETH1
ip route add 192.168.101.0/24 via 192.168.100.2
ip -n ns0 route add 192.168.100.0/24 via 192.168.101.2
./net-next/samples/pktgen/pktgen_sample03_burst_single_flow.sh -i $ETH0 -s 64 -m 00:04:9f:05:de:0a -d 192.168.101.1 -t 2 -f 13 -c 0 -p 400 -n 0 -b 4

I compiled the commands from some notes I had lying around, I didn't
retest them.