netdev - Re: HTB accuracy on 10GbE

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Message-ID: <4AF1660E.1080401@gmail.com>
Date:	Wed, 04 Nov 2009 12:31:26 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ryousei Takano <ryousei@...il.com>
CC:	Stephen Hemminger <shemminger@...tta.com>,
	Patrick McHardy <kaber@...sh.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	takano-ryousei@...t.go.jp
Subject: Re: HTB accuracy on 10GbE

Ryousei Takano a écrit :

> 
> I tried iperf with 60 seconds samples. I got the almost same result.
> 
> Here is the result:
>       sender	receiver
> 1.000 1.00	1.00
> 2.000 2.01	2.01
> 3.000 3.03	3.02
> 4.000 4.07	4.07
> 5.000 5.05	5.05
> 6.000 6.16	6.16
> 7.000 7.22	7.22
> 8.000 8.15	8.15
> 9.000 9.23	9.23
> 9.900 9.69	9.69
> 

One thing to consider is the estimation error in qdisc_l2t(), rate table has only 256 slots

static inline u32 qdisc_l2t(struct qdisc_rate_table* rtab, unsigned int pktlen)
{
	int slot = pktlen + rtab->rate.cell_align + rtab->rate.overhead;
	if (slot < 0)
		slot = 0;
	slot >>= rtab->rate.cell_log;
	if (slot > 255)
		return (rtab->data[255]*(slot >> 8) + rtab->data[slot & 0xFF]);
	return rtab->data[slot];
}


Maybe you can try changing class mtu to 40000 instead of 9000, and quantum to 60000 too

tc class add dev $DEV parent 1: classid 1:1 htb rate ${rate}mbit mtu 40000 quantum 60000

(because your tcp stack sends large buffers ( ~ 60000 bytes) as your NIC can offload tcp segmentation)

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