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

["Song, Yoong Siang" <yoong.siang.song@intel.com>]

On Wednesday, January 8, 2025 12:58 AM, Stanislav Fomichev <stfomichev@gmail.com> wrote:
>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 <yoong.siang.song@intel.com>
>> ---
>>  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..

Agree that your code is more readable.
I will use your suggestion in next version.

Thanks & Regards
Siang