[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 21/03/2023 19.45, Stanislav Fomichev wrote:
> On Tue, Mar 21, 2023 at 6:32 AM Jesper Dangaard Brouer
> <jbrouer@redhat.com> wrote:
>>
>>
>>
>> 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.
> 
> SG. If you prefer to keep the comment let's also s/outout/outPut/.

Sorry, missed this... will fix in V3

> 
>>> 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?
> 
> On the recent kernels I think this event has to be explicitly enabled
> for bpf_prink() to work? Not sure.

The output still work for me then I have zero in 
/sys/kernel/debug/tracing/events/bpf_trace/bpf_trace_printk/enable

> That's why having something like enable_tracing() and dump_trace()
> here might be helpful for whoever is running the prog.
>