On 04/18, Jesper Dangaard Brouer wrote: > 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: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> Acked-by: Stanislav Fomichev <sdf@xxxxxxxxxx> > --- > .../testing/selftests/bpf/progs/xdp_hw_metadata.c | 4 +- > tools/testing/selftests/bpf/xdp_hw_metadata.c | 47 ++++++++++++++++++-- > tools/testing/selftests/bpf/xdp_metadata.h | 1 > 3 files changed, 46 insertions(+), 6 deletions(-) > > diff --git a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c > index e1c787815e44..b2dfd7066c6e 100644 > --- a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c > +++ b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c > @@ -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(); nit: why not set it unconditionally? > + 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); > diff --git a/tools/testing/selftests/bpf/xdp_hw_metadata.c b/tools/testing/selftests/bpf/xdp_hw_metadata.c > index 987cf0db5ebc..613321eb84c1 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" > > @@ -134,18 +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) > diff --git a/tools/testing/selftests/bpf/xdp_metadata.h b/tools/testing/selftests/bpf/xdp_metadata.h > index 0c4624dc6f2f..938a729bd307 100644 > --- a/tools/testing/selftests/bpf/xdp_metadata.h > +++ b/tools/testing/selftests/bpf/xdp_metadata.h > @@ -11,6 +11,7 @@ > > struct xdp_meta { > __u64 rx_timestamp; > + __u64 xdp_timestamp; > __u32 rx_hash; > union { > __u32 rx_hash_type; > >
