| Message ID | 167906360589.2706833.6188844928251441787.stgit@firesoul (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | XDP-hints kfuncs for Intel driver igc | expand |
On 03/17, 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) > 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@redhat.com> Acked-by: Stanislav Fomichev <sdf@google.com> With a small nit below. > --- > .../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 */ Nit: curly braces around else {} block as well? > 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; > };
On 17/03/2023 22.09, Stanislav Fomichev wrote: >> 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 */ > > Nit: curly braces around else {} block as well? Good point, fixed in V2
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; };
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@redhat.com> --- .../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(-)