Acked-by: Ivo Calado <ivocalado@embedded.ufcg.edu.br>  for ccid4 subtree

On Mon, Aug 16, 2010 at 02:19, Gerrit Renker <gerrit@erg.abdn.ac.uk> wrote:
quoted text
> This patch relates to the similar one submitted last week for CCID-2.
>
> It replaces the hardcoded (Kconfig) value of the minimum RTO value with
> a reconfigurable, per-route value which falls back to the TCP minimum
> RTO value.
>
> Leando, Ivo, can you please have a look and indicate whether you are ok
> with this? If yes I would like to also update the CCID-4 tree to make it
> consistent with the test tree - for this reason the test tree has not yet
> been updated.
>
>>>>>>>>>>>>>>>>>>>>>>>> Patch <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
> dccp ccid-3: use per-route RTO or TCP RTO as fallback
>
> This makes the TCP (per-route) RTO value also available to CCID-3, hence it
> is now possible to influence this value at runtime rather than, as before,
> via Kconfig.
>
> The same effect as the default Kconfig option of 100ms is now achieved by
>
>> ip route replace to unicast 192.168.0.0/24 rto_min 100j dev eth0
>
> (assuming HZ=1000).
>
> Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
> ---
>  net/dccp/ccids/Kconfig |   31 -------------------------------
>  net/dccp/ccids/ccid3.c |    9 ++++-----
>  2 files changed, 4 insertions(+), 36 deletions(-)
>
> --- a/net/dccp/ccids/Kconfig
> +++ b/net/dccp/ccids/Kconfig
> @@ -47,37 +47,6 @@ config IP_DCCP_CCID3_DEBUG
>
>          If in doubt, say N.
>
> -config IP_DCCP_CCID3_RTO
> -         int "Use higher bound for nofeedback timer"
> -         default 100
> -         depends on IP_DCCP_CCID3 && EXPERIMENTAL
> -         ---help---
> -           Use higher lower bound for nofeedback timer expiration.
> -
> -           The TFRC nofeedback timer normally expires after the maximum of 4
> -           RTTs and twice the current send interval (RFC 3448, 4.3). On LANs
> -           with a small RTT this can mean a high processing load and reduced
> -           performance, since then the nofeedback timer is triggered very
> -           frequently.
> -
> -           This option enables to set a higher lower bound for the nofeedback
> -           value. Values in units of milliseconds can be set here.
> -
> -           A value of 0 disables this feature by enforcing the value specified
> -           in RFC 3448. The following values have been suggested as bounds for
> -           experimental use:
> -               * 16-20ms to match the typical multimedia inter-frame interval
> -               * 100ms as a reasonable compromise [default]
> -               * 1000ms corresponds to the lower TCP RTO bound (RFC 2988, 2.4)
> -
> -           The default of 100ms is a compromise between a large value for
> -           efficient DCCP implementations, and a small value to avoid disrupting
> -           the network in times of congestion.
> -
> -           The purpose of the nofeedback timer is to slow DCCP down when there
> -           is serious network congestion: experimenting with larger values should
> -           therefore not be performed on WANs.
> -
>  config IP_DCCP_TFRC_LIB
>        def_bool y if IP_DCCP_CCID3
>
> --- a/net/dccp/ccids/ccid3.c
> +++ b/net/dccp/ccids/ccid3.c
> @@ -461,12 +461,11 @@ done_computing_x:
>
>        /*
>         * Update timeout interval for the nofeedback timer.
> -        * We use a configuration option to increase the lower bound.
> -        * This can help avoid triggering the nofeedback timer too
> -        * often ('spinning') on LANs with small RTTs.
> +        * We use the current (per-route) value of the TCP RTO as lower bound
> +        * to slow down rate-halving on networks with small RTTs (loopback,
> +        * running DCCP in a virtual machine, Gbit ethernet, etc).
>         */
> -       hc->tx_t_rto = max_t(u32, 4 * hc->tx_rtt, (CONFIG_IP_DCCP_CCID3_RTO *
> -                                                      (USEC_PER_SEC / 1000)));
> +       hc->tx_t_rto = max(4 * hc->tx_rtt, USEC_PER_SEC/HZ * tcp_rto_min(sk));
>        /*
>         * Schedule no feedback timer to expire in
>         * max(t_RTO, 2 * s/X)  =  max(t_RTO, 2 * t_ipi)
>



-- 
Ivo Augusto Andrade Rocha Calado
PhD candidate in Electrical Engineering
Embedded Systems and Pervasive Computing Lab - http://embedded.ufcg.edu.br
Electrical Engineering Department - http://dee.ufcg.edu.br/
Electrical Engineering and Informatics Center - http://www.ceei.ufcg.edu.br
Federal University of Campina Grande - http://www.ufcg.edu.br

PGP: 0xD7C3860A pgp.mit.edu
Putt's Law:
       Technology is dominated by two types of people:
               Those who understand what they do not manage.
               Those who manage what they do not understand.
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