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

From: Stanislav Fomichev <[email-masked]>
Date: Fri, 17 Mar 2023 14:13:16 -0700

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 <[email-masked]>

Acked-by: Stanislav Fomichev <[email-masked]>

(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/progs/xdp_hw_metadata.c  
> b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> index f2a3b70a9882..f2278ca2ad03 100644
> --- a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> +++ b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> @@ -76,10 +76,13 @@ int rx(struct xdp_md *ctx)
>   	} else
>   		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

Maybe we should just dump the contents of
/sys/kernel/debug/tracing/trace for every poll cycle?

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 :-)

> + *
>    * 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) {