netdev - Re: [PATCH] net_sched: restore "mpu xxx" handling

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Message-ID: <1438175068.20182.90.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 29 Jul 2015 15:04:28 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Kirill Tkhai <ktkhai@...n.com>
Cc:	netdev@...r.kernel.org, Jesper Dangaard Brouer <brouer@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>, tkhai@...ru
Subject: Re: [PATCH] net_sched: restore "mpu xxx" handling

On Wed, 2015-07-29 at 14:24 +0300, Kirill Tkhai wrote:
> commit 56b765b79 ("htb: improved accuracy at high rates")
> broke the "mpu xxx" handling.
> 
> This patch restores the "mpu xxx" handling for htb:
> 
> # tc class add dev eth0 classid 1:2 parent 1: htb rate 1mbit mpu 0
> # ping -f -c 1000 10.30.22.52
> rtt min/avg/max/mdev = 0.156/1.881/2.454/0.175 ms, ipg/ewma 1.908/1.925 ms
> 
> # tc class change dev eth0 classid 1:2 parent 1: htb rate 1mbit mpu 1000
> # ping -f -c 1000 10.30.22.52
> rtt min/avg/max/mdev = 15.352/22.229/38.646/2.212 ms, pipe 3, ipg/ewma 15.999/22.609 ms

Note this mpu option was completely broken a long time ago with GSO /
TSO anyway.

Note sure we really want it in this state ?

What is your use case ?

In any case, correct fix would be in psched_l2t_ns(), otherwise you fix
htb but not the other qdisc (tbf for that matter)



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