netdev - Re: [PATCH 1/2] udp: add tracepoints for queueing skb to rcvbuf

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Message-ID: <5b828bb3667480edda9a4a77918007ee@localhost>
Date:	Tue, 21 Jun 2011 16:48:39 +0200
From:	Hagen Paul Pfeifer <hagen@...u.net>
To:	Neil Horman <nhorman@...driver.com>
Cc:	Satoru Moriya <satoru.moriya@....com>, <netdev@...r.kernel.org>,
	Seiji Aguchi <seiji.aguchi@....com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 1/2] udp:  add tracepoints for queueing skb to rcvbuf

On Tue, 21 Jun 2011 09:50:09 -0400, Neil Horman wrote:

> I hadn't really thought about that much, but yes, I suppose I could
migrate
> dropwatch to export kfree_skb data via perf.  Admittedly I don't know
much
> about
> the perf api.  Do you have any pointers on its use (to save me time in
> figuring
> out how it all works)?  If so I'll start looking into it.

http://git.kernel.org/?p=status/powertop/powertop.git;a=tree;f=perf;hb=HEAD

is probably a good starting point. Especially
perf_bundle.cpp:handle_trace_point(). But I am not sure if this is the most
clever way. The direct us of the perf api is somewhat dodgy (not sure if
the ABI will change). IIRC Steven Rostedt wrote about a user space library
(I CC'ed Steven). BUT: tracing via /sys/kernel/debug/tracing/* may be
enough, eventually there is no need for perf at all. Then trace-cmd may
provide some nice ideas how to wrap the /sys/kernel/debug/tracing interface
programmatically.

The idea behind dropwatch is great! There is currently to much
unconsolidated information. It takes a genius to understand where and later
why packets are dropped. A userspace tool where no kernel patch is required
is a big plus! ;-)

Hagen
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