netdev - Re: [PATCH V2 1/1 (was 0/1 by accident)] tools/dtrace: initial implementation of DTrace

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Date:   Wed, 10 Jul 2019 14:49:52 -0700
From:   Brendan Gregg <brendan.d.gregg@...il.com>
To:     Kris Van Hees <kris.van.hees@...cle.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Jonathan Corbet <corbet@....net>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, dtrace-devel@....oracle.com,
        LKML <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Chris Mason <clm@...com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH V2 1/1 (was 0/1 by accident)] tools/dtrace: initial
 implementation of DTrace

On Wed, Jul 10, 2019 at 2:36 PM Kris Van Hees <kris.van.hees@...cle.com> wrote:
>
> On Wed, Jul 10, 2019 at 11:19:43PM +0200, Daniel Borkmann wrote:
> > On 07/10/2019 10:30 PM, Jonathan Corbet wrote:
> > > On Wed, 10 Jul 2019 21:32:25 +0200
> > > Daniel Borkmann <daniel@...earbox.net> wrote:
> > >
> > >> Looks like you missed Brendan Gregg's prior feedback from v1 [0]. I haven't
> > >> seen a strong compelling argument for why this needs to reside in the kernel
> > >> tree given we also have all the other tracing tools and many of which also
> > >> rely on BPF such as bcc, bpftrace, ply, systemtap, sysdig, lttng to just name
> > >> a few.
> > >
> > > So I'm just watching from the sidelines here, but I do feel the need to
> > > point out that Kris appears to be trying to follow the previous feedback
> > > he got from Alexei, where creating tools/dtrace is exactly what he was
> > > told to do:
> > >
> > >   https://lwn.net/ml/netdev/20190521175617.ipry6ue7o24a2e6n@ast-mbp.dhcp.thefacebook.com/
> > >
> > > Now he's being told the exact opposite.  Not the best experience for
> > > somebody who is trying to make the kernel better.
> >
> > Ugh, agree, sorry for the misleading direction. Alexei is currently offgrid
> > this week, he might comment later.
> >
> > It has nothing to do with making the _kernel_ better, it's a /user space/ front
> > end for the existing kernel infrastructure like many of the other tracers out
> > there. Don't get me wrong, adding the missing /kernel parts/ for it is a totally
> > different subject [and _that_ is what is making the kernel better, not the former].
>
> I disagree.  Yes, the current patch obviously isn't making the kernel better
> because it doesn't touch the kernel.  But DTrace as a whole is not just a
> /front end/ to the existing kernel infrastructure, and I did make that point
> at LPC 2018 and in my emails.  Some of its more advanced features will lead
> to contributions to the kernel that (by virtue of being developed as part of
> this DTrace re-implementation) will more often than not be able to benefit
> other tracers as well.  I do think that aspect qualifies as working towards
> making the kenrel better.
>
> > Hypothetical question: does it make the _kernel_ better if we suddenly add a huge
> > and complex project like tools/mysql/ to the kernel tree? Nope.
> >
> > > There are still people interested in DTrace out there.  How would you
> > > recommend that Kris proceed at this point?
> >
> > My recommendation to proceed is to maintain the dtrace user space tooling in
> > its own separate project like the vast majority of all the other tracing projects
> > (see also the other advantages that Steven pointed out from his experience), and
> > extend the kernel bits whenever needed.
>
> I wish that would have been the initial recommendation because it certainly
> would have avoided me going down a path that was going to lead to rejection.
>
> Either way, I do hope that as work progresses and contributions to the kernel
> code are submitted in support of advancing tracing on Linux, those patches
> will receive a fair review and consideration.  I can appreciate that some
> people do not like DTrace or feel that it is not necessary, but personal
> opinions about tools should not be a deciding factor in whether a contribution
> has merit or not.

Hey Kris -- so you're referring to me, and I've used DTrace more than
anyone over the past 15 years, and I don't think anyone has used all
the different Linux tracers more than I have. I think my opinion has a
lot of value.


Brendan