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) xsk_ring_cons__peek: 1 0x11fc958: rx_desc[7]->addr=10000000000f000 addr=f100 comp_addr=f000 rx_hash: 0x00000000 rx_timestamp: 1676297171760293047 (sec:1676297171.7603) XDP RX-time: 1676297208760355863 (sec:1676297208.7604) delta sec:37.0001 AF_XDP time: 1676297208760416292 (sec:1676297208.7604) delta sec:0.0001 (60.429 usec) 0x11fc958: complete idx=15 addr=f000 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 60 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: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> --- .../testing/selftests/bpf/progs/xdp_hw_metadata.c | 8 ++- tools/testing/selftests/bpf/xdp_hw_metadata.c | 46 ++++++++++++++++++-- tools/testing/selftests/bpf/xdp_metadata.h | 1 3 files changed, 47 insertions(+), 8 deletions(-) diff --git a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c index 4c55b4d79d3d..f2a3b70a9882 100644 --- a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c +++ b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c @@ -69,9 +69,11 @@ int rx(struct xdp_md *ctx) return XDP_PASS; } - if (!bpf_xdp_metadata_rx_timestamp(ctx, &meta->rx_timestamp)) - bpf_printk("populated rx_timestamp with %llu", meta->rx_timestamp); - else + if (!bpf_xdp_metadata_rx_timestamp(ctx, &meta->rx_timestamp)) { + meta->xdp_timestamp = bpf_ktime_get_tai_ns(); + bpf_printk("populated rx_timestamp with %llu", meta->rx_timestamp); + bpf_printk("populated xdp_timestamp with %llu", meta->xdp_timestamp); + } else meta->rx_timestamp = 0; /* Used by AF_XDP as not avail signal */ if (!bpf_xdp_metadata_rx_hash(ctx, &meta->rx_hash)) diff --git a/tools/testing/selftests/bpf/xdp_hw_metadata.c b/tools/testing/selftests/bpf/xdp_hw_metadata.c index 1c8acb68b977..400bfe19abfe 100644 --- a/tools/testing/selftests/bpf/xdp_hw_metadata.c +++ b/tools/testing/selftests/bpf/xdp_hw_metadata.c @@ -27,6 +27,7 @@ #include <sys/mman.h> #include <net/if.h> #include <poll.h> +#include <time.h> #include "xdp_metadata.h" @@ -134,14 +135,47 @@ 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); printf("rx_hash: %u\n", meta->rx_hash); + 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) @@ -189,7 +223,7 @@ 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]; @@ -237,7 +271,8 @@ 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); } @@ -364,6 +399,7 @@ 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; @@ -437,7 +473,7 @@ 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) diff --git a/tools/testing/selftests/bpf/xdp_metadata.h b/tools/testing/selftests/bpf/xdp_metadata.h index f6780fbb0a21..260345b2c6f1 100644 --- a/tools/testing/selftests/bpf/xdp_metadata.h +++ b/tools/testing/selftests/bpf/xdp_metadata.h @@ -11,5 +11,6 @@ struct xdp_meta { __u64 rx_timestamp; + __u64 xdp_timestamp; __u32 rx_hash; };
