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

[Jesper Dangaard Brouer <jbrouer@redhat.com>]

On 21/03/2023 19.47, Stanislav Fomichev wrote:
> On Tue, Mar 21, 2023 at 6:47 AM Jesper Dangaard Brouer
> <brouer@redhat.com> 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@redhat.com>
>> ---
>>   .../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@google.com>
> 
>> + *
>>    * 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) {
>>
>>
>