Subject: Re: [PATCH bpf-next v4 2/4] selftests/bpf: Add Launch Time request to xdp_hw_metadata

From: Stanislav Fomichev <[email-masked]>
Date: Tue, 7 Jan 2025 08:57:35 -0800

On 01/06, Song Yoong Siang wrote:
> Add Launch Time hw offload request to xdp_hw_metadata. User can configure
> the delta of launch time to HW RX-time by using "-l" argument. The default
> delta is 100,000,000 nanosecond.
> 
> Signed-off-by: Song Yoong Siang <[email-masked]>
> ---
>  tools/testing/selftests/bpf/xdp_hw_metadata.c | 30 +++++++++++++++++--
>  1 file changed, 27 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/xdp_hw_metadata.c b/tools/testing/selftests/bpf/xdp_hw_metadata.c
> index 6f7b15d6c6ed..795c1d14e02d 100644
> --- a/tools/testing/selftests/bpf/xdp_hw_metadata.c
> +++ b/tools/testing/selftests/bpf/xdp_hw_metadata.c
> @@ -13,6 +13,7 @@
>   * - UDP 9091 packets trigger TX reply
>   * - TX HW timestamp is requested and reported back upon completion
>   * - TX checksum is requested
> + * - TX launch time HW offload is requested for transmission
>   */
>  
>  #include <test_progs.h>
> @@ -64,6 +65,8 @@ int rxq;
>  bool skip_tx;
>  __u64 last_hw_rx_timestamp;
>  __u64 last_xdp_rx_timestamp;
> +__u64 last_launch_time;
> +__u64 launch_time_delta_to_hw_rx_timestamp = 100000000; /* 0.1 second */
>  
>  void test__fail(void) { /* for network_helpers.c */ }
>  
> @@ -298,6 +301,8 @@ static bool complete_tx(struct xsk *xsk, clockid_t clock_id)
>  	if (meta->completion.tx_timestamp) {
>  		__u64 ref_tstamp = gettime(clock_id);
>  
> +		print_tstamp_delta("HW Launch-time", "HW TX-complete-time",
> +				   last_launch_time, meta->completion.tx_timestamp);
>  		print_tstamp_delta("HW TX-complete-time", "User TX-complete-time",
>  				   meta->completion.tx_timestamp, ref_tstamp);
>  		print_tstamp_delta("XDP RX-time", "User TX-complete-time",
> @@ -395,6 +400,14 @@ static void ping_pong(struct xsk *xsk, void *rx_packet, clockid_t clock_id)
>  	       xsk, ntohs(udph->check), ntohs(want_csum),
>  	       meta->request.csum_start, meta->request.csum_offset);
>  
> +	/* Set the value of launch time */
> +	meta->flags |= XDP_TXMD_FLAGS_LAUNCH_TIME;
> +	meta->request.launch_time = last_hw_rx_timestamp +
> +				    launch_time_delta_to_hw_rx_timestamp;
> +	last_launch_time = meta->request.launch_time;
> +	print_tstamp_delta("HW RX-time", "HW Launch-time", last_hw_rx_timestamp,
> +			   meta->request.launch_time);
> +
>  	memcpy(data, rx_packet, len); /* don't share umem chunk for simplicity */
>  	tx_desc->options |= XDP_TX_METADATA;
>  	tx_desc->len = len;
> @@ -402,10 +415,14 @@ static void ping_pong(struct xsk *xsk, void *rx_packet, clockid_t clock_id)
>  	xsk_ring_prod__submit(&xsk->tx, 1);
>  }
>  
> +#define SLEEP_PER_ITERATION_IN_US 10
> +#define SLEEP_PER_ITERATION_IN_NS (SLEEP_PER_ITERATION_IN_US * 1000)
> +#define MAX_ITERATION(x) (((x) / SLEEP_PER_ITERATION_IN_NS) + 500)
>  static int verify_metadata(struct xsk *rx_xsk, int rxq, int server_fd, clockid_t clock_id)
>  {
>  	const struct xdp_desc *rx_desc;
>  	struct pollfd fds[rxq + 1];
> +	int max_iterations;
>  	__u64 comp_addr;
>  	__u64 addr;
>  	__u32 idx = 0;
> @@ -418,6 +435,9 @@ static int verify_metadata(struct xsk *rx_xsk, int rxq, int server_fd, clockid_t
>  		fds[i].revents = 0;
>  	}
>  
> +	/* Calculate max iterations to wait for transmit completion */
> +	max_iterations = MAX_ITERATION(launch_time_delta_to_hw_rx_timestamp);
> +
>  	fds[rxq].fd = server_fd;
>  	fds[rxq].events = POLLIN;
>  	fds[rxq].revents = 0;
> @@ -477,10 +497,10 @@ static int verify_metadata(struct xsk *rx_xsk, int rxq, int server_fd, clockid_t
>  					if (ret)
>  						printf("kick_tx ret=%d\n", ret);
>  

[..]

> -					for (int j = 0; j < 500; j++) {
> +					for (int j = 0; j < max_iterations; j++) {
>  						if (complete_tx(xsk, clock_id))
>  							break;
> -						usleep(10);
> +						usleep(SLEEP_PER_ITERATION_IN_US);

nit: instead of doing MAX_ITERATION/max_iterations, can we simplify this
to the following?

static u64 now(void)
{
	clock_gettime(...);
	return ts.tv_sec * NSEC_PER_SEC + ts.tv_nsec;
}

/* wait 5 seconds + cover launch time */
deadline = now() + 5 * NSEC_PER_SEC + launch_time_delta_to_hw_rx_timestamp;
while (true) {
	if (complete_tx())
		break;
	if (now() >= deadline)
		break;
	usleep(10);
}

It is a bit more readable than converting time to wait to the
iterations..