netdev - Re: [PATCH net-next] netem: slotting with non-uniform distribution

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Message-Id: <20180628.220700.2197626700312750888.davem@davemloft.net>
Date:   Thu, 28 Jun 2018 22:07:00 +0900 (KST)
From:   David Miller <davem@...emloft.net>
To:     ysseung@...gle.com
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net-next] netem: slotting with non-uniform distribution

From: Yousuk Seung <ysseung@...gle.com>
Date: Wed, 27 Jun 2018 10:32:19 -0700

> Extend slotting with support for non-uniform distributions. This is
> similar to netem's non-uniform distribution delay feature.
> 
> Commit f043efeae2f1 ("netem: support delivering packets in delayed
> time slots") added the slotting feature to approximate the behaviors
> of media with packet aggregation but only supported a uniform
> distribution for delays between transmission attempts. Tests with TCP
> BBR with emulated wifi links with non-uniform distributions produced
> more useful results.
> 
> Syntax:
>    slot dist DISTRIBUTION DELAY JITTER [packets MAX_PACKETS] \
>       [bytes MAX_BYTES]
> 
> The syntax and use of the distribution table is the same as in the
> non-uniform distribution delay feature. A file DISTRIBUTION must be
> present in TC_LIB_DIR (e.g. /usr/lib/tc) containing numbers scaled by
> NETEM_DIST_SCALE. A random value x is selected from the table and it
> takes DELAY + ( x * JITTER ) as delay. Correlation between values is not
> supported.
> 
> Examples:
>   Normal distribution delay with mean = 800us and stdev = 100us.
>   > tc qdisc add dev eth0 root netem slot dist normal 800us 100us
> 
>   Optionally set the max slot size in bytes and/or packets.
>   > tc qdisc add dev eth0 root netem slot dist normal 800us 100us \
>     bytes 64k packets 42
> 
> Signed-off-by: Yousuk Seung <ysseung@...gle.com>
> Acked-by: Eric Dumazet <edumazet@...gle.com>
> Acked-by: Neal Cardwell <ncardwell@...gle.com>

Applied.