From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alexei Starovoitov <ast@fb.com>
Subject: Re: [PATCH v7 bpf-next 06/10] tracepoint: compute num_args at build
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Date: Wed, 28 Mar 2018 11:19:34 -0700
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To: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, "David S. Miller" <davem@davemloft.net>, Daniel Borkmann <daniel@iogearbox.net>, Linus Torvalds <torvalds@linux-foundation.org>, Peter Zijlstra <peterz@infradead.org>, netdev <netdev@vger.kernel.org>, kernel-team <kernel-team@fb.com>, linux-api <linux-api@vger.kernel.org>, Josh Poimboeuf <jpoimboe@redhat.com>
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On 3/28/18 11:10 AM, Steven Rostedt wrote:
> On Wed, 28 Mar 2018 11:03:24 -0700
> Alexei Starovoitov <ast@fb.com> wrote:
>
>> I can live with this overhead if Mathieu insists,
>> but I prefer to keep it in 'struct tracepoint'.
>>
>> Thoughts?
>
> I'm fine with keeping it as is. We could probably use it for future
> enhancements in perf and ftrace.
>
> Perhaps, we should just add a:
>
> #ifdef CONFIG_BPF_EVENTS
>
> Around the use cases of num_args.

it sounds like a good idea, but implementation wise
it will be ifdef CONFIG_BPF_EVENTS around u32 num_args;
in struct tracepoint and similar double definition of
DEFINE_TRACE_FN. One that uses num_args to init
struct tracepoint and one that doesn't ?
Feels like serious uglification of already macros heavy code.
Also what it will address?
cache hot/cold argument clearly doesn't apply.