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

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Message-ID: <1328545089.2200.13.camel@gandalf.stny.rr.com>
Date:	Mon, 06 Feb 2012 11:18:09 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Neil Horman <nhorman@...driver.com>
Cc:	"Frank Ch. Eigler" <fche@...hat.com>,
	Hagen Paul Pfeifer <hagen@...u.net>,
	"Frank Ch. Eigler" <fche@...stic.org>,
	Satoru Moriya <satoru.moriya@....com>,
	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"tgraf@...radead.org" <tgraf@...radead.org>,
	"stephen.hemminger@...tta.com" <stephen.hemminger@...tta.com>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>,
	Seiji Aguchi <seiji.aguchi@....com>, fche@...rceware.org,
	mathieu.desnoyers@...ymtl.ca
Subject: Re: [PATCH v2 0/2] Tracepoint for tcp retransmission

On Mon, 2012-02-06 at 10:53 -0500, Neil Horman wrote:

> Yes, that was his point.  Mine was that, given Satoru's needs, a netfilter hook
> provides 90% of what they need (as its been described here).  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.  They're what iptables/ip6tables/ebtables/etc use to do everything they
> do.  I'm suggesting that they use those existing hooks to monitor outgoing
> traffic for whatever information they want (in this case retransmitted unacked
> tcp sequence numbers).  Or whatever else their interested in.
> 
> As for the other 10% (recording failed retransmits, which don't generate
> traffic), we have existing tracepoints that can be used.

I haven't looked at the details here, but I'm wondering if netfilter
could benefit from static_branch() calls (aka jump-labels). I'm sure
selinux could too. Basically, when netfilter is disabled, the fast path
would just include a nop, with no if() branch testing at all. When you
enable netfilters, it would then add a jmp to the code that actually
does the tests.

-- Steve


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