netdev - Re: [RFC PATCH net-next 0/5] tcp: TCP tracer

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Date:	Mon, 15 Dec 2014 08:03:15 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Laurent Chavey <chavey@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>
Cc:	Martin KaFai Lau <kafai@...com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Lawrence Brakmo <brakmo@...com>, Josef Bacik <jbacik@...com>,
	Kernel Team <Kernel-team@...com>
Subject: Re: [RFC PATCH net-next 0/5] tcp: TCP tracer

On Sun, 2014-12-14 at 22:55 -0800, Alexei Starovoitov wrote:

> I think patches 1 and 3 are good additions, since they establish
> few permanent points of instrumentation in tcp stack.
> Patches 4-5 look more like use cases of tracepoints established
> before. They may feel like simple additions and, no doubt,
> they are useful, but since they expose things via tracing
> infra they become part of api and cannot be changed later,
> when more stats would be needed.
> I think systemtap like scripting on top of patches 1 and 3
> should solve your use case ?
> Also, have you looked at recent eBPF work?
> Though it's not completely ready yet, soon it should
> be able to do the same stats collection as you have
> in 4/5 without adding permanent pieces to the kernel.

So it looks like web10g like interfaces are very often requested by
various teams.

And we have many different views on how to hack this. I am astonished by
number of hacks I saw about this stuff going on.

What about a clean way, extending current TCP_INFO, which is both
available as a getsockopt() for socket owners and ss/iproute2
information for 'external entities'

If we consider web10g info needed, then adding a ftrace/eBPF like
interface is simply yet another piece of code we need to maintain,
and the argument of 'this should cost nothing if not activated' is
nonsense since major players need to constantly monitor TCP metrics and
behavior.

It seems both FaceBook and Google are working on a subset of web10g.

I suggest we meet together and establish a common ground, preferably
after Christmas holidays.

Thanks


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