[xdp-hints] Re: [PATCH bpf-next V1 4/7] selftests/bpf: xdp_hw_metadata RX hash return code info

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

On 17/03/2023 22.13, Stanislav Fomichev wrote:
> On 03/17, Jesper Dangaard Brouer 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>
> 
> Acked-by: Stanislav Fomichev <sdf@google.com>
> 
> (with a small suggestion below, maybe can do separately?)
> 
>> ---
>>   .../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/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
> 
> Maybe we should just dump the contents of
> /sys/kernel/debug/tracing/trace for every poll cycle?
> 

I think this belongs to a separate patch.

> We can also maybe enable tracing in this program transparently?
> I usually forget 'echo 1 >
> /sys/kernel/debug/tracing/events/bpf_trace/bpf_trace_printk/enable'
> myself :-)
> 
What is this trick?

--Jesper