Subject: Re: [PATCH v2 bpf-next 1/2] xdp: Add tracepoint for bulk XDP_TX

From: Jesper Dangaard Brouer <[email-masked]>
Date: Wed, 5 Jun 2019 09:59:31 +0200

On Wed,  5 Jun 2019 14:36:12 +0900
Toshiaki Makita <[email-masked]> wrote:

> This is introduced for admins to check what is happening on XDP_TX when
> bulk XDP_TX is in use, which will be first introduced in veth in next
> commit.

Is the plan that this tracepoint 'xdp:xdp_bulk_tx' should be used by
all drivers?

(more below)

> Signed-off-by: Toshiaki Makita <[email-masked]>
> ---
>  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,
> +
> +	TP_PROTO(const struct net_device *dev,
> +		 int sent, int drops, int err),
> +
> +	TP_ARGS(dev, sent, drops, err),
> +
> +	TP_STRUCT__entry(

All other tracepoints in this file starts with:

		__field(int, prog_id)
		__field(u32, act)
or
		__field(int, map_id)
		__field(u32, act)

Could you please add those?

> +		__field(int, ifindex)
> +		__field(int, drops)
> +		__field(int, sent)
> +		__field(int, err)
> +	),

The reason is that this make is easier to attach to multiple
tracepoints, and extract the same value.

Example with bpftrace oneliner:

$ sudo bpftrace -e 'tracepoint:xdp:xdp_* { @action[args->act] = count(); }'
Attaching 8 probes...
^C

@action[4]: 30259246
@action[0]: 34489024

XDP_ABORTED = 0 	 
XDP_REDIRECT= 4

> +
> +	TP_fast_assign(

		__entry->act		= XDP_TX;

> +		__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)
> +);
> +

Other fun bpftrace stuff:

sudo bpftrace -e 'tracepoint:xdp:xdp_*map* { @map_id[comm, args->map_id] = count(); }'
Attaching 5 probes...
^C

@map_id[swapper/2, 113]: 1428
@map_id[swapper/0, 113]: 2085
@map_id[ksoftirqd/4, 113]: 2253491
@map_id[ksoftirqd/2, 113]: 25677560
@map_id[ksoftirqd/0, 113]: 29004338
@map_id[ksoftirqd/3, 113]: 31034885

$ bpftool map list id 113
113: devmap  name tx_port  flags 0x0
	key 4B  value 4B  max_entries 100  memlock 4096B

p.s. People should look out for Brendan Gregg's upcoming book on BPF
performance tools, from which I learned to use bpftrace :-)
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer