Subject: Re: [PATCH v2 0/2] Tracepoint for tcp retransmission

From: "Frank Ch. Eigler" <[email-masked]>
Date: Mon, 6 Feb 2012 11:21:36 -0500

Hi -

On Mon, Feb 06, 2012 at 10:53:05AM -0500, Neil Horman wrote:

> [...] If you're unfamiliar with them, netfilter hooks are those
> standard points in the network input/output/forwarding paths at
> which we can watch and maniupulate network traffic.  [...]

Aha, nf_register_hook and friends.  Thanks for the pointer.

> > Does this mean that this netfilter hook mechanism is sufficient to
> > adapt to the current/future diversity of behaviors?  Why not make
> > *that* into a tracepoint then, so perf/stap scripts could get at it in
> > userspace?

> I suppose you could.  [...]  I'm suggesting a kernel module because
> then you wouldn't have the performance overhead of moving all those
> frames to user space.

(For what it's worth, if there were a tracepoint in the netfilter 
hook machinery, stap would be able to process the packets likewise,
in-kernel, with no kernel debuginfo installed.)

- FChE