netdev - Re: [PATCH net-next] tcp: add tcpi_segs_in and tcpi_segs_out to tcp

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Message-ID: <1432238760.4060.104.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 21 May 2015 13:06:00 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Yuchung Cheng <ycheng@...gle.com>
Cc:	Marcelo Ricardo Leitner <mleitner@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Matt Mathis <mattmathis@...gle.com>,
	Craig Gallek <cgallek@...gle.com>, Martin Lau <kafai@...com>,
	Chris Rapier <rapier@....edu>
Subject: Re: [PATCH net-next] tcp: add tcpi_segs_in and tcpi_segs_out to
 tcp_info

On Thu, 2015-05-21 at 12:41 -0700, Yuchung Cheng wrote:

> It'd be nice to count SYN and SYNACKs for apps tracking the handshake stats.
> For syn-cookies we can't do much. But for the rest we can account
> req->num_retrans for SYN-ACKs sent, and perhaps track SYN received in
> request sock?

Well, this is partly because we can not guarantee the behavior that I
chose to explicitly state that we were not tracking SYNACK for passive
sessions.

Also TCP_DEFER_ACCEPT comes into play here...

If we want to handle this in a deterministic way, we would have to add
some bit to warn the application reading tcp_info that the session was
initiated after a valid syncookie was received, and that initial value
of tcp_info.tcpi_segs_{in|out} can be wrong.



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