netdev - Re: [PATCH v7 bpf-next 06/10] tracepoint: compute num

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Message-ID: <20180328145431.687643bc@gandalf.local.home>
Date:   Wed, 28 Mar 2018 14:54:31 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexei Starovoitov <ast@...com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        netdev <netdev@...r.kernel.org>,
        kernel-team <kernel-team@...com>,
        linux-api <linux-api@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v7 bpf-next 06/10] tracepoint: compute num_args at build
 time

On Wed, 28 Mar 2018 11:19:34 -0700
Alexei Starovoitov <ast@...com> wrote:

> On 3/28/18 11:10 AM, Steven Rostedt wrote:
> > On Wed, 28 Mar 2018 11:03:24 -0700
> > Alexei Starovoitov <ast@...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?

32bit bloat ;-)

But I agree, it's not worth uglifying it.

-- Steve

> cache hot/cold argument clearly doesn't apply.