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

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Message-ID: <1328547754.2220.86.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Mon, 06 Feb 2012 18:02:34 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Neil Horman <nhorman@...driver.com>,
	"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>,
	Seiji Aguchi <seiji.aguchi@....com>, fche@...rceware.org,
	mathieu.desnoyers@...ymtl.ca
Subject: Re: [PATCH v2 0/2] Tracepoint for tcp retransmission

Le lundi 06 février 2012 à 11:18 -0500, Steven Rostedt a écrit :
> 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.

Hmm... I thought I already did that.

Or maybe I intended so and forgot.

Ah no, its there in commit a2d7ec58ac09
(netfilter: use jump_label for nf_hooks)



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