[bpf-next,2/3] xdp: Add tracepoint for bulk XDP_TX

This is introduced for admins to check what is happening on XDP_TX when
bulk XDP_TX is in use.

Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
---
 include/trace/events/xdp.h | 25 +++++++++++++++++++++++++
 kernel/bpf/core.c          |  1 +
 2 files changed, 26 insertions(+)

On Thu, 23 May 2019 19:56:47 +0900
Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp> wrote:

> This is introduced for admins to check what is happening on XDP_TX when
> bulk XDP_TX is in use.
> 
> Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
> ---
>  include/trace/events/xdp.h | 25 +++++++++++++++++++++++++
>  kernel/bpf/core.c          |  1 +
>  2 files changed, 26 insertions(+)
> 
> diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
> index e95cb86..e06ea65 100644
> --- a/include/trace/events/xdp.h
> +++ b/include/trace/events/xdp.h
> @@ -50,6 +50,31 @@
>  		  __entry->ifindex)
>  );
>  
> +TRACE_EVENT(xdp_bulk_tx,
> +

You are using this tracepoint like/instead of trace_xdp_devmap_xmit if
I understand correctly?  Or maybe the trace_xdp_redirect tracepoint.

The point is that is will be good if the tracepoints can share the
TP_STRUCT layout beginning, as it allows for attaching and reusing eBPF
code that is only interested in the top part of the struct.

I would also want to see some identifier, that trace programs can use
to group and corrolate these events, you do have ifindex, but most
other XDP tracepoints also have "prog_id".

> +	TP_PROTO(const struct net_device *dev,
> +		 int sent, int drops, int err),
> +
> +	TP_ARGS(dev, sent, drops, err),
> +
> +	TP_STRUCT__entry(
> +		__field(int, ifindex)
> +		__field(int, drops)
> +		__field(int, sent)
> +		__field(int, err)
> +	),

The xdp_redirect_template have:

	TP_STRUCT__entry(
		__field(int, prog_id)
		__field(u32, act)
		__field(int, ifindex)
		__field(int, err)
		__field(int, to_ifindex)
		__field(u32, map_id)
		__field(int, map_index)
	),

And e.g. TRACE_EVENT xdp_exception have:

	TP_STRUCT__entry(
		__field(int, prog_id)
		__field(u32, act)
		__field(int, ifindex)
	),


> +
> +	TP_fast_assign(
> +		__entry->ifindex	= dev->ifindex;
> +		__entry->drops		= drops;
> +		__entry->sent		= sent;
> +		__entry->err		= err;
> +	),
> +
> +	TP_printk("ifindex=%d sent=%d drops=%d err=%d",
> +		  __entry->ifindex, __entry->sent, __entry->drops, __entry->err)
> +);
> +
>  DECLARE_EVENT_CLASS(xdp_redirect_template,
>  
>  	TP_PROTO(const struct net_device *dev,
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 242a643..7687488 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2108,3 +2108,4 @@ int __weak skb_copy_bits(const struct sk_buff *skb, int offset, void *to,
>  #include <linux/bpf_trace.h>
>  
>  EXPORT_TRACEPOINT_SYMBOL_GPL(xdp_exception);
> +EXPORT_TRACEPOINT_SYMBOL_GPL(xdp_bulk_tx);

On 2019/05/23 22:12, Jesper Dangaard Brouer wrote:
> On Thu, 23 May 2019 19:56:47 +0900
> Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp> wrote:
> 
>> This is introduced for admins to check what is happening on XDP_TX when
>> bulk XDP_TX is in use.
>>
>> Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
>> ---
>>  include/trace/events/xdp.h | 25 +++++++++++++++++++++++++
>>  kernel/bpf/core.c          |  1 +
>>  2 files changed, 26 insertions(+)
>>
>> diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
>> index e95cb86..e06ea65 100644
>> --- a/include/trace/events/xdp.h
>> +++ b/include/trace/events/xdp.h
>> @@ -50,6 +50,31 @@
>>  		  __entry->ifindex)
>>  );
>>  
>> +TRACE_EVENT(xdp_bulk_tx,
>> +
> 
> You are using this tracepoint like/instead of trace_xdp_devmap_xmit if
> I understand correctly?  Or maybe the trace_xdp_redirect tracepoint.

Yes, I have trace_xdp_devmap_xmit in mind, which is for XDP_REDIRECT.

> The point is that is will be good if the tracepoints can share the
> TP_STRUCT layout beginning, as it allows for attaching and reusing eBPF
> code that is only interested in the top part of the struct.

It's good, but this tracepoint does not have map concept so differs from
xdp_devmap_xmit.

> I would also want to see some identifier, that trace programs can use
> to group and corrolate these events, you do have ifindex, but most
> other XDP tracepoints also have "prog_id".

I have considered that too. The problem is that we cannot pass a
reliable prog_id since bulk xmit happens after RCU critical section of
XDP_TX.
xdp_devmap_xmit does not have prog_id and I guess there is a similar
reason for it?