Subject: Re: [PATCH net-next v4 2/2] selftests: virtio_net: add buffer circulation test

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 5 Feb 2026 01:24:37 -0500

On Wed, Feb 04, 2026 at 11:36:17AM -0800, Vishwanath Seshagiri wrote:
> Add iperf3-based test to verify RX buffer handling under load.
> Optionally logs page_pool tracepoints when available.

but it doesn't verify/validate them - it's just a generic throughput
test. so what is the value add here?

> Signed-off-by: Vishwanath Seshagiri <[email-masked]>
> ---
>  .../drivers/net/virtio_net/basic_features.sh  | 86 +++++++++++++++++++
>  1 file changed, 86 insertions(+)
> 
> diff --git a/tools/testing/selftests/drivers/net/virtio_net/basic_features.sh b/tools/testing/selftests/drivers/net/virtio_net/basic_features.sh
> index cf8cf816ed48..fa98505c4674 100755
> --- a/tools/testing/selftests/drivers/net/virtio_net/basic_features.sh
> +++ b/tools/testing/selftests/drivers/net/virtio_net/basic_features.sh
> @@ -6,6 +6,7 @@
>  ALL_TESTS="
>  	initial_ping_test
>  	f_mac_test
> +	buffer_circulation_test
>  "
>  
>  source virtio_net_common.sh
> @@ -16,6 +17,8 @@ source "$lib_dir"/../../../net/forwarding/lib.sh
>  h1=${NETIFS[p1]}
>  h2=${NETIFS[p2]}
>  
> +IPERF_SERVER_PID=""
> +
>  h1_create()
>  {
>  	simple_if_init $h1 $H1_IPV4/24 $H1_IPV6/64
> @@ -83,6 +86,84 @@ f_mac_test()
>  	log_test "$test_name"
>  }
>  
> +buffer_circulation_test()
> +{
> +	RET=0
> +	local test_name="buffer circulation"
> +	local tracefs="/sys/kernel/tracing"
> +
> +	if ! check_command iperf3; then
> +		log_test_skip "$test_name" "iperf3 not installed"
> +		return 0
> +	fi
> +
> +	setup_cleanup
> +	setup_prepare
> +
> +	ping -c 1 -I "$h1" "$H2_IPV4" >/dev/null
> +	if [ $? -ne 0 ]; then
> +		check_err 1 "Ping failed"
> +		log_test "$test_name"
> +		return
> +	fi
> +
> +	local rx_start=$(cat /sys/class/net/"$h2"/statistics/rx_packets)
> +	local tx_start=$(cat /sys/class/net/"$h1"/statistics/tx_packets)
> +
> +	if [ -d "$tracefs/events/page_pool" ]; then
> +		echo > "$tracefs/trace"
> +		echo 1 > "$tracefs/events/page_pool/enable"
> +	fi
> +
> +	local port=$(shuf -i 49152-65535 -n 1)
> +
> +	iperf3 -s -1 --bind-dev "$h2" -p "$port" &>/dev/null &
> +	IPERF_SERVER_PID=$!
> +	sleep 1
> +
> +	if ! kill -0 "$IPERF_SERVER_PID" 2>/dev/null; then
> +		IPERF_SERVER_PID=""
> +		if [ -d "$tracefs/events/page_pool" ]; then
> +			echo 0 > "$tracefs/events/page_pool/enable"
> +		fi
> +		check_err 1 "iperf3 server died"
> +		log_test "$test_name"
> +		return
> +	fi
> +
> +	iperf3 -c "$H2_IPV4" --bind-dev "$h1" -p "$port" -t 5 >/dev/null 2>&1
> +	local iperf_ret=$?
> +
> +	if [ -n "$IPERF_SERVER_PID" ]; then
> +		kill "$IPERF_SERVER_PID" 2>/dev/null || true
> +		wait "$IPERF_SERVER_PID" 2>/dev/null || true
> +		IPERF_SERVER_PID=""
> +	fi
> +
> +	if [ -d "$tracefs/events/page_pool" ]; then
> +		echo 0 > "$tracefs/events/page_pool/enable"
> +		local trace="$tracefs/trace"
> +		local hold=$(grep -c "page_pool_state_hold" "$trace" 2>/dev/null)
> +		local release=$(grep -c "page_pool_state_release" "$trace" 2>/dev/null)
> +		log_info "page_pool events: hold=${hold:-0}, release=${release:-0}"
> +	fi
> +
> +	local rx_end=$(cat /sys/class/net/"$h2"/statistics/rx_packets)
> +	local tx_end=$(cat /sys/class/net/"$h1"/statistics/tx_packets)
> +	local rx_delta=$((rx_end - rx_start))
> +	local tx_delta=$((tx_end - tx_start))
> +
> +	log_info "Circulated TX:$tx_delta RX:$rx_delta"
> +
> +	if [ "$iperf_ret" -ne 0 ]; then
> +		check_err 1 "iperf3 failed"
> +	elif [ "$rx_delta" -lt 10000 ]; then
> +		check_err 1 "Too few packets: $rx_delta"
> +	fi
> +
> +	log_test "$test_name"
> +}
> +
>  setup_prepare()
>  {
>  	virtio_device_rebind $h1
> @@ -113,6 +194,11 @@ setup_cleanup()
>  
>  cleanup()
>  {
> +	if [ -n "$IPERF_SERVER_PID" ]; then
> +		kill "$IPERF_SERVER_PID" 2>/dev/null || true
> +		wait "$IPERF_SERVER_PID" 2>/dev/null || true
> +	fi
> +
>  	pre_cleanup
>  	setup_cleanup
>  }
> -- 
> 2.47.3