Subject: Re: [PATCH net-next] sch_red: Adaptative RED AQM

From: Stephen Hemminger <[email-masked]>
Date: Thu, 8 Dec 2011 09:21:30 -0800

On Thu, 08 Dec 2011 17:06:03 +0100
Eric Dumazet <[email-masked]> wrote:

> Changes against our RED implementation are :
> 
> max_p is no longer a negative power of two (1/(2^Plog)), but a Q0.32
> fixed point number, to allow full range described in Adatative paper.
> 
> To deliver a random number, we now use a reciprocal divide (thats really
> a multiply), but this operation is done once per marked/droped packet
> when in RED_BETWEEN_TRESH window, so added cost (compared to previous
> AND operation) is near zero.
> 
> dump operation gives current max_p value in a new TCA_RED_MAX_P
> attribute.
> 
> Example on a 10Mbit link :
> 
> tc qdisc add dev $DEV parent 1:1 handle 10: est 1sec 8sec red \
>    limit 400000 min 30000 max 90000 avpkt 1000 \
>    burst 55 ecn adaptative bandwidth 10Mbit
> 
> # tc -s -d qdisc show dev eth3
> ...
> qdisc red 10: parent 1:1 limit 400000b min 30000b max 90000b ecn
> adaptative ewma 5 max_p=0.113335 Scell_log 15
>  Sent 50414282 bytes 34504 pkt (dropped 35, overlimits 1392 requeues 0) 
>  rate 9749Kbit 831pps backlog 72056b 16p requeues 0 
>   marked 1357 early 35 pdrop 0 other 0
> 
> 
> Signed-off-by: Eric Dumazet <[email-masked]>

Is this backward compatible for users that don't specify
an adaptive parameter.
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