netdev - Re: [PATCH] netem: fix delay calculation in rate extension

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Date:	Tue, 29 Jan 2013 16:03:08 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	jn@...sta.de
Cc:	netdev@...r.kernel.org, hagen@...u.net
Subject: Re: [PATCH] netem: fix delay calculation in rate extension

From: Johannes Naab <jn@...sta.de>
Date: Wed, 23 Jan 2013 22:36:51 +0100

> From: Johannes Naab <jn@...sta.de>
> 
> The delay calculation with the rate extension introduces in v3.3 does
> not properly work, if other packets are still queued for transmission.
> For the delay calculation to work, both delay types (latency and delay
> introduces by rate limitation) have to be handled differently. The
> latency delay for a packet can overlap with the delay of other packets.
> The delay introduced by the rate however is separate, and can only
> start, once all other rate-introduced delays finished.
> 
> Latency delay is from same distribution for each packet, rate delay
> depends on the packet size.
> 
> .: latency delay
> -: rate delay
> x: additional delay we have to wait since another packet is currently
>    transmitted
> 
>   .....----                    Packet 1
>     .....xx------              Packet 2
>                .....------     Packet 3
>     ^^^^^
>     latency stacks
>          ^^
>          rate delay doesn't stack
>                ^^
>                latency stacks
>  
>   -----> time
> 
> When a packet is enqueued, we first consider the latency delay. If other
> packets are already queued, we can reduce the latency delay until the
> last packet in the queue is send, however the latency delay cannot be
> <0, since this would mean that the rate is overcommitted.  The new
> reference point is the time at which the last packet will be send. To
> find the time, when the packet should be send, the rate introduces delay
> has to be added on top of that.
> 
> Signed-off-by: Johannes Naab <jn@...sta.de>
> Acked-by: Hagen Paul Pfeifer <hagen@...u.net>

Applied, thanks.
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