Commit bb323478 authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by Daniel Borkmann
Browse files

selftests/bpf: xdp_hw_metadata track more timestamps 

To correlate the hardware RX timestamp with something, add tracking of
two software timestamps both clock source CLOCK_TAI (see description in
man clock_gettime(2)).

XDP metadata is extended with xdp_timestamp for capturing when XDP
received the packet. Populated with BPF helper bpf_ktime_get_tai_ns(). I
could not find a BPF helper for getting CLOCK_REALTIME, which would have
been preferred. In userspace when AF_XDP sees the packet another
software timestamp is recorded via clock_gettime() also clock source
CLOCK_TAI.

Example output shortly after loading igc driver:

  poll: 1 (0) skip=1 fail=0 redir=2
  xsk_ring_cons__peek: 1
  0x12557a8: rx_desc[1]->addr=100000000009000 addr=9100 comp_addr=9000
  rx_hash: 0x82A96531 with RSS type:0x1
  rx_timestamp:  1681740540304898909 (sec:1681740540.3049)
  XDP RX-time:   1681740577304958316 (sec:1681740577.3050) delta sec:37.0001 (37000059.407 usec)
  AF_XDP time:   1681740577305051315 (sec:1681740577.3051) delta sec:0.0001 (92.999 usec)
  0x12557a8: complete idx=9 addr=9000

The first observation is that the 37 sec difference between RX HW vs XDP
timestamps, which indicate hardware is likely clock source
CLOCK_REALTIME, because (as of this writing) CLOCK_TAI is initialised
with a 37 sec offset.

The 93 usec (microsec) difference between XDP vs AF_XDP userspace is the
userspace wakeup time. On this hardware it was caused by CPU idle sleep
states, which can be reduced by tuning /dev/cpu_dma_latency.

View current requested/allowed latency bound via:
  hexdump --format '"%d\n"' /dev/cpu_dma_latency

More explanation of the output and how this can be used to identify
clock drift for the HW clock can be seen here[1]:

[1] https://github.com/xdp-project/xdp-project/blob/master/areas/hints/xdp_hints_kfuncs02_driver_igc.org



Signed-off-by: default avatarJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarStanislav Fomichev <sdf@google.com>
Acked-by: default avatarSong Yoong Siang <yoong.siang.song@intel.com>
Link: https://lore.kernel.org/bpf/168182466298.616355.2544377890818617459.stgit@firesoul
parent d6772667

tools/testing/selftests/bpf/progs/xdp_hw_metadata.c

+3 −1
Original line number Diff line number Diff line
@@ -77,7 +77,9 @@ int rx(struct xdp_md *ctx) 
	}



	err = bpf_xdp_metadata_rx_timestamp(ctx, &meta->rx_timestamp);

	if (err)

	if (!err)

		meta->xdp_timestamp = bpf_ktime_get_tai_ns();

	else

		meta->rx_timestamp = 0; /* Used by AF_XDP as not avail signal */



	err = bpf_xdp_metadata_rx_hash(ctx, &meta->rx_hash, &meta->rx_hash_type);

tools/testing/selftests/bpf/xdp_hw_metadata.c

+42 −5
Original line number Diff line number Diff line
@@ -27,6 +27,7 @@ 
#include <sys/mman.h>

#include <net/if.h>

#include <poll.h>

#include <time.h>



#include "xdp_metadata.h"
@@ -134,18 +135,52 @@ static void refill_rx(struct xsk *xsk, __u64 addr) 
	}

}



static void verify_xdp_metadata(void *data)

#define NANOSEC_PER_SEC 1000000000 /* 10^9 */

static __u64 gettime(clockid_t clock_id)

{

	struct timespec t;

	int res;



	/* See man clock_gettime(2) for type of clock_id's */

	res = clock_gettime(clock_id, &t);



	if (res < 0)

		error(res, errno, "Error with clock_gettime()");



	return (__u64) t.tv_sec * NANOSEC_PER_SEC + t.tv_nsec;

}



static void verify_xdp_metadata(void *data, clockid_t clock_id)

{

	struct xdp_meta *meta;



	meta = data - sizeof(*meta);



	printf("rx_timestamp: %llu\n", meta->rx_timestamp);

	if (meta->rx_hash_err < 0)

		printf("No rx_hash err=%d\n", meta->rx_hash_err);

	else

		printf("rx_hash: 0x%X with RSS type:0x%X\n",

		       meta->rx_hash, meta->rx_hash_type);



	printf("rx_timestamp:  %llu (sec:%0.4f)\n", meta->rx_timestamp,

	       (double)meta->rx_timestamp / NANOSEC_PER_SEC);

	if (meta->rx_timestamp) {

		__u64 usr_clock = gettime(clock_id);

		__u64 xdp_clock = meta->xdp_timestamp;

		__s64 delta_X = xdp_clock - meta->rx_timestamp;

		__s64 delta_X2U = usr_clock - xdp_clock;



		printf("XDP RX-time:   %llu (sec:%0.4f) delta sec:%0.4f (%0.3f usec)\n",

		       xdp_clock, (double)xdp_clock / NANOSEC_PER_SEC,

		       (double)delta_X / NANOSEC_PER_SEC,

		       (double)delta_X / 1000);



		printf("AF_XDP time:   %llu (sec:%0.4f) delta sec:%0.4f (%0.3f usec)\n",

		       usr_clock, (double)usr_clock / NANOSEC_PER_SEC,

		       (double)delta_X2U / NANOSEC_PER_SEC,

		       (double)delta_X2U / 1000);

	}



}



static void verify_skb_metadata(int fd)
@@ -193,7 +228,7 @@ static void verify_skb_metadata(int fd) 
	printf("skb hwtstamp is not found!\n");

}



static int verify_metadata(struct xsk *rx_xsk, int rxq, int server_fd)

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];
@@ -243,7 +278,8 @@ static int verify_metadata(struct xsk *rx_xsk, int rxq, int server_fd) 
			addr = xsk_umem__add_offset_to_addr(rx_desc->addr);

			printf("%p: rx_desc[%u]->addr=%llx addr=%llx comp_addr=%llx\n",

			       xsk, idx, rx_desc->addr, addr, comp_addr);

			verify_xdp_metadata(xsk_umem__get_data(xsk->umem_area, addr));

			verify_xdp_metadata(xsk_umem__get_data(xsk->umem_area, addr),

					    clock_id);

			xsk_ring_cons__release(&xsk->rx, 1);

			refill_rx(xsk, comp_addr);

		}
@@ -370,6 +406,7 @@ static void timestamping_enable(int fd, int val) 


int main(int argc, char *argv[])

{

	clockid_t clock_id = CLOCK_TAI;

	int server_fd = -1;

	int ret;

	int i;
@@ -443,7 +480,7 @@ int main(int argc, char *argv[]) 
		error(1, -ret, "bpf_xdp_attach");



	signal(SIGINT, handle_signal);

	ret = verify_metadata(rx_xsk, rxq, server_fd);

	ret = verify_metadata(rx_xsk, rxq, server_fd, clock_id);

	close(server_fd);

	cleanup();

	if (ret)

tools/testing/selftests/bpf/xdp_metadata.h

+1 −0
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 


struct xdp_meta {

	__u64 rx_timestamp;

	__u64 xdp_timestamp;

	__u32 rx_hash;

	union {

		__u32 rx_hash_type;