Re: [PATCH bpf-next V2 3/6] selftests/bpf: xdp_hw_metadata RX hash return code info

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On 21/03/2023 19.47, Stanislav Fomichev wrote:
On Tue, Mar 21, 2023 at 6:47 AM Jesper Dangaard Brouer
<brouer@xxxxxxxxxx> wrote:

When driver developers add XDP-hints kfuncs for RX hash it is
practical to print the return code in bpf_printk trace pipe log.

Print hash value as a hex value, both AF_XDP userspace and bpf_prog,
as this makes it easier to spot poor quality hashes.

Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
---
  .../testing/selftests/bpf/progs/xdp_hw_metadata.c  |    9 ++++++---
  tools/testing/selftests/bpf/xdp_hw_metadata.c      |    5 ++++-
  2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
index 40c17adbf483..ce07010e4d48 100644
--- a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
+++ b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
@@ -77,10 +77,13 @@ int rx(struct xdp_md *ctx)
                 meta->rx_timestamp = 0; /* Used by AF_XDP as not avail signal */
         }

-       if (!bpf_xdp_metadata_rx_hash(ctx, &meta->rx_hash))
-               bpf_printk("populated rx_hash with %u", meta->rx_hash);
-       else
+       ret = bpf_xdp_metadata_rx_hash(ctx, &meta->rx_hash);
+       if (ret >= 0) {
+               bpf_printk("populated rx_hash with 0x%08X", meta->rx_hash);
+       } else {
+               bpf_printk("rx_hash not-avail errno:%d", ret);
                 meta->rx_hash = 0; /* Used by AF_XDP as not avail signal */
+       }

         return bpf_redirect_map(&xsk, ctx->rx_queue_index, XDP_PASS);
  }
diff --git a/tools/testing/selftests/bpf/xdp_hw_metadata.c b/tools/testing/selftests/bpf/xdp_hw_metadata.c
index 400bfe19abfe..f3ec07ccdc95 100644
--- a/tools/testing/selftests/bpf/xdp_hw_metadata.c
+++ b/tools/testing/selftests/bpf/xdp_hw_metadata.c
@@ -3,6 +3,9 @@
  /* Reference program for verifying XDP metadata on real HW. Functional test
   * only, doesn't test the performance.
   *
+ * BPF-prog bpf_printk info outout can be access via
+ * /sys/kernel/debug/tracing/trace_pipe

s/outout/output/


Fixed in V3

But let's maybe drop it? If you want to make it more usable, let's
have a separate patch to enable tracing and periodically dump it to
the console instead (as previously discussed).

Cat'ing /sys/kernel/debug/tracing/trace_pipe work for me regardless of
setting in
/sys/kernel/debug/tracing/events/bpf_trace/bpf_trace_printk/enable

We likely need a followup patch that adds a BPF config switch that can
disable bpf_printk calls, because this adds overhead and thus affects
the timestamps.

With this addressed:
Acked-by: Stanislav Fomichev <sdf@xxxxxxxxxx>

+ *
   * RX:
   * - UDP 9091 packets are diverted into AF_XDP
   * - Metadata verified:
@@ -156,7 +159,7 @@ static void verify_xdp_metadata(void *data, clockid_t clock_id)

         meta = data - sizeof(*meta);

-       printf("rx_hash: %u\n", meta->rx_hash);
+       printf("rx_hash: 0x%08X\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) {







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