netdev - Re: [PATCH v2 net-next] tcp: Fix CWV being too strict on thin streams

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Date:	Wed, 23 Sep 2015 14:37:58 -0400
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Bendik Rønning Opstad <bro.devel@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Netdev <netdev@...r.kernel.org>,
	Bendik Rønning Opstad <bro.devel+kernel@...il.com>,
	Andreas Petlund <apetlund@...ula.no>,
	Carsten Griwodz <griff@...ula.no>,
	Jonas Markussen <jonassm@....uio.no>,
	Kenneth Klette Jonassen <kennetkl@....uio.no>,
	Mads Johannessen <madsjoh@....uio.no>
Subject: Re: [PATCH v2 net-next] tcp: Fix CWV being too strict on thin streams

On Wed, Sep 23, 2015 at 12:49 PM, Bendik Rønning Opstad
<bro.devel@...il.com> wrote:
> Application limited streams such as thin streams, that transmit small
> amounts of payload in relatively few packets per RTT, can be prevented
> from growing the CWND when in congestion avoidance. This leads to
> increased sojourn times for data segments in streams that often transmit
> time-dependent data.
>
> Currently, a connection is considered CWND limited only after having
> successfully transmitted at least one packet with new data, while at the
> same time failing to transmit some unsent data from the output queue
> because the CWND is full. Applications that produce small amounts of
> data may be left in a state where it is never considered to be CWND
> limited, because all unsent data is successfully transmitted each time
> an incoming ACK opens up for more data to be transmitted in the send
> window.
>
> Fix by always testing whether the CWND is fully used after successful
> packet transmissions, such that a connection is considered CWND limited
> whenever the CWND has been filled. This is the correct behavior as
> specified in RFC2861 (section 3.1).
>
> Cc: Andreas Petlund <apetlund@...ula.no>
> Cc: Carsten Griwodz <griff@...ula.no>
> Cc: Jonas Markussen <jonassm@....uio.no>
> Cc: Kenneth Klette Jonassen <kennetkl@....uio.no>
> Cc: Mads Johannessen <madsjoh@....uio.no>
> Signed-off-by: Bendik Rønning Opstad <bro.devel+kernel@...il.com>
> ---

Acked-by: Neal Cardwell <ncardwell@...gle.com>
Tested-by: Neal Cardwell <ncardwell@...gle.com>

I ran all the Google packetdrill test cases with this patched in, and
all still pass.

I also re-ran the test I posted in the v1 thread (based on Eric's
test), and it still passes.

neal
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