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Re: [Xen-devel] Linux Traffic Shaping broken in 3.0.3rc1 ?

  • To: Timo Benk <Timo.Benk@xxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
  • Date: Mon, 09 Oct 2006 16:40:56 +0100
  • Delivery-date: Mon, 09 Oct 2006 08:41:29 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcbruU9ijgJS5lesEdulPAAX8io7RQ==
  • Thread-topic: [Xen-devel] Linux Traffic Shaping broken in 3.0.3rc1 ?

On 7/10/06 20:21, "Timo Benk" <Timo.Benk@xxxxxx> wrote:

> with Xen 3.0.2 i used tc to limit the outgoing traffic rate and it
> worked very well and accurate with the HTB class:
> Limit: 1mbit / actual rate: 116.2KB/s (given by scp)
> Now i looked at 3.0.3rc1 and noticed that traffic shaping using the same
> setup as before does not work as accurate as before (same hardware):
> Limit: 1mbit / actual rate: 449.0KB/s (given by scp)

This is not a Xen-specific bug. The problem is that now we support TSO,
packets are larger than the maximum that TC expects and so we overflow the
pre-computed rate table (and our 8kB packets get treated as 1.6kB packets).
To see this, run 'tc -s class show dev peth0'. You'll see a 'giants' field
that is non-zero -- those are all packets that were too big to handle

The fix is simple. Add an explicit mtu parameter to the htb class:
tc class add dev peth0 parent 1:0 classid 1:1 htb rate 1mbit mtu 16000


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