Hi Vladimir,

On Thu Apr 28 2022, Vladimir Oltean wrote:
> The Felix VSC9959 switch in NXP LS1028A supports the tc-gate action
> which enforced time-based access control per stream. A stream as seen by
> this switch is identified by {MAC DA, VID}.
>
> We use the standard forwarding selftest topology with 2 host interfaces
> and 2 switch interfaces. The host ports must require timestamping non-IP
> packets and supporting tc-etf offload, for isochron to work. The
> isochron program monitors network sync status (ptp4l, phc2sys) and
> deterministically transmits packets to the switch such that the tc-gate
> action either (a) always accepts them based on its schedule, or
> (b) always drops them.
>
> I tried to keep as much of the logic that isn't specific to the NXP
> LS1028A in a new tsn_lib.sh, for future reuse. This covers
> synchronization using ptp4l and phc2sys, and isochron.

For running this selftest `isochron` tool is required. That's neither
packaged on Linux distributions or available in the kernel source. I
guess, it has to be built from your Github account/repository?

>
> The cycle-time chosen for this selftest isn't particularly impressive
> (and the focus is the functionality of the switch), but I didn't really
> know what to do better, considering that it will mostly be run during
> debugging sessions, various kernel bloatware would be enabled, like
> lockdep, KASAN, etc, and we certainly can't run any races with those on.
>
> I tried to look through the kselftest framework for other real time
> applications and didn't really find any, so I'm not sure how better to
> prepare the environment in case we want to go for a lower cycle time.
> At the moment, the only thing the selftest is ensuring is that dynamic
> frequency scaling is disabled on the CPU that isochron runs on. It would
> probably be useful to have a blacklist of kernel config options (checked
> through zcat /proc/config.gz) and some cyclictest scripts to run
> beforehand, but I saw none of those.
>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

[snip]

> diff --git a/tools/testing/selftests/net/forwarding/tsn_lib.sh b/tools/testing/selftests/net/forwarding/tsn_lib.sh
> new file mode 100644
> index 000000000000..efac5badd5a0
> --- /dev/null
> +++ b/tools/testing/selftests/net/forwarding/tsn_lib.sh
> @@ -0,0 +1,219 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright 2021-2022 NXP
> +
> +# Tunables
> +UTC_TAI_OFFSET=37

Why do you need the UTC to TAI offset? isochron could just use CLOCK_TAI
as clockid for the task scheduling.

> +ISOCHRON_CPU=1

Seems reasonable to assume two cpus.

> +
> +# https://github.com/vladimiroltean/tsn-scripts
> +# WARNING: isochron versions pre-1.0 are unstable,
> +# always use the latest version
> +require_command isochron
> +require_command phc2sys
> +require_command ptp4l
> +
> +phc2sys_start()
> +{
> +	local if_name=$1
> +	local uds_address=$2
> +	local extra_args=""
> +
> +	if ! [ -z "${uds_address}" ]; then
> +		extra_args="${extra_args} -z ${uds_address}"
> +	fi
> +
> +	phc2sys_log="$(mktemp)"
> +
> +	chrt -f 10 phc2sys -m \
> +		-c ${if_name} \
> +		-s CLOCK_REALTIME \
> +		-O ${UTC_TAI_OFFSET} \
> +		--step_threshold 0.00002 \
> +		--first_step_threshold 0.00002 \
> +		${extra_args} \
> +		> "${phc2sys_log}" 2>&1 &
> +	phc2sys_pid=$!
> +
> +	echo "phc2sys logs to ${phc2sys_log} and has pid ${phc2sys_pid}"
> +
> +	sleep 1
> +}
> +
> +phc2sys_stop()
> +{
> +	{ kill ${phc2sys_pid} && wait ${phc2sys_pid}; } 2> /dev/null
> +	rm "${phc2sys_log}" 2> /dev/null
> +}
> +
> +ptp4l_start()
> +{
> +	local if_name=$1
> +	local slave_only=$2
> +	local uds_address=$3
> +	local log="ptp4l_log_${if_name}"
> +	local pid="ptp4l_pid_${if_name}"
> +	local extra_args=""
> +
> +	if [ "${slave_only}" = true ]; then
> +		extra_args="${extra_args} -s"
> +	fi
> +
> +	# declare dynamic variables ptp4l_log_${if_name} and ptp4l_pid_${if_name}
> +	# as global, so that they can be referenced later
> +	declare -g "${log}=$(mktemp)"
> +
> +	chrt -f 10 ptp4l -m -2 -P \
> +		-i ${if_name} \
> +		--step_threshold 0.00002 \
> +		--first_step_threshold 0.00002 \
> +		--tx_timestamp_timeout 100 \
> +		--uds_address="${uds_address}" \
> +		${extra_args} \
> +		> "${!log}" 2>&1 &
> +	declare -g "${pid}=$!"
> +
> +	echo "ptp4l for interface ${if_name} logs to ${!log} and has pid ${!pid}"
> +
> +	sleep 1
> +}
> +
> +ptp4l_stop()
> +{
> +	local if_name=$1
> +	local log="ptp4l_log_${if_name}"
> +	local pid="ptp4l_pid_${if_name}"
> +
> +	{ kill ${!pid} && wait ${!pid}; } 2> /dev/null
> +	rm "${!log}" 2> /dev/null
> +}
> +
> +cpufreq_max()
> +{
> +	local cpu=$1
> +	local freq="cpu${cpu}_freq"
> +	local governor="cpu${cpu}_governor"
> +
> +	# declare dynamic variables cpu${cpu}_freq and cpu${cpu}_governor as
> +	# global, so they can be referenced later
> +	declare -g "${freq}=$(cat /sys/bus/cpu/devices/cpu${cpu}/cpufreq/scaling_min_freq)"
> +	declare -g "${governor}=$(cat /sys/bus/cpu/devices/cpu${cpu}/cpufreq/scaling_governor)"
> +
> +	cat /sys/bus/cpu/devices/cpu${cpu}/cpufreq/scaling_max_freq > \
> +		/sys/bus/cpu/devices/cpu${cpu}/cpufreq/scaling_min_freq
> +	echo -n "performance" > \
> +		/sys/bus/cpu/devices/cpu${cpu}/cpufreq/scaling_governor
> +}
> +
> +cpufreq_restore()
> +{
> +	local cpu=$1
> +	local freq="cpu${cpu}_freq"
> +	local governor="cpu${cpu}_governor"
> +
> +	echo "${!freq}" > /sys/bus/cpu/devices/cpu${cpu}/cpufreq/scaling_min_freq
> +	echo -n "${!governor}" > \
> +		/sys/bus/cpu/devices/cpu${cpu}/cpufreq/scaling_governor
> +}
> +
> +isochron_recv_start()
> +{
> +	local if_name=$1
> +	local uds=$2
> +	local extra_args=$3
> +
> +	if ! [ -z "${uds}" ]; then
> +		extra_args="--unix-domain-socket ${uds}"
> +	fi
> +
> +	isochron rcv \
> +		--interface ${if_name} \
> +		--sched-priority 98 \
> +		--sched-rr \

Why SCHED_RR?

Thanks,
Kurt