Re: NET_SCHED cbq dropping too many packets on a bonding interface

["Kingsley Foreman" <kingsley@internode.com.au>]

--------------------------------------------------
From: "Eric Dumazet" <dada1@cosmosbay.com>
Sent: Thursday, May 15, 2008 2:51 PM
To: "Kingsley Foreman" <kingsley@internode.com.au>
Cc: "Andrew Morton" <akpm@linux-foundation.org>; 
<linux-kernel@vger.kernel.org>; <netdev@vger.kernel.org>
Subject: Re: NET_SCHED cbq dropping too many packets on a bonding interface

> Andrew Morton a écrit :
>> (cc netdev)
>>
>> On Thu, 15 May 2008 12:25:19 +0930 "Kingsley Foreman" 
>> <kingsley@internode.com.au> wrote:
>>
>>
>>> Ive been using qdisc for quite a while without any problems,
>>> I just rebuilt a gentoo box with 2.6.25 kernel that does a lot of 
>>> traffic
>>> ~1000mbits+ over a bonded interface
>>>
>>> Im however seeing a big problem with cbq class dropping packets for no
>>> reason i can see, and it is causing a lot of speed issues.
>>>
>>> the basic config is this
>>> _____________________________________________________________________
>>> /sbin/tc qdisc del dev bond0 root
>>> /sbin/tc qdisc add dev bond0 root handle 1 cbq bandwidth 2000Mbit avpkt 
>>> 1000
>>> cell 8
>>> /sbin/tc class change dev bond0 root cbq weight 200Mbit allot 1514
>>>
>>> /sbin/tc class add dev bond0 parent 1: classid 1:1280 cbq bandwidth 
>>> 2000Mbit
>>> rate 1200Mbit weight 120Mbit prio 1 allot 1514 cell 8 maxburst 120 
>>> minburst
>>> 1 minidle 0 avpkt 1000 bounded
>>> /sbin/tc filter add dev bond0 parent 1:0 protocol ip prio 300 route to 5
>>> classid 1:1280
>>>
>>> /sbin/tc class add dev bond0 parent 1: classid 1:1281 cbq bandwidth 
>>> 2000Mbit
>>> rate 400Mbit weight 40Mbit prio 6 allot 1514 cell 8 maxburst 120 
>>> minburst 1
>>> minidle 0 avpkt 1000 bounded
>>> /sbin/tc filter add dev bond0 parent 1:0 protocol ip prio 300 route to 6
>>> classid 1:1281
>>> ____________________________________________________________________
>>>
>>> So there is a lot of bandwidth handed out but it is still dropping a lot 
>>> of
>>> packets  for very small ammounts of traffic eg 300mbits.
>>>
>>> However the biggest problem im seeing is if i just do this
>>>
>>> __________________________________________________________________
>>> /sbin/tc qdisc del dev bond0 root
>>> /sbin/tc qdisc add dev bond0 root handle 1 cbq bandwidth 2000Mbit avpkt 
>>> 1000
>>> cell 8
>>> /sbin/tc class change dev bond0 root cbq weight 200Mbit allot 1514
>>> ___________________________________________________________________
>>>
>>> after 30sec I get results like
>>> ___________________________________________________________________
>>>
>>> ### bond0: queueing disciplines
>>>
>>> qdisc cbq 1: root rate 2000Mbit (bounded,isolated) prio no-transmit
>>>  Sent 574230043 bytes 407156 pkt (dropped 2524, overlimits 0 requeues 0)
>>>  rate 0bit 0pps backlog 0b 0p requeues 0
>>>   borrowed 0 overactions 0 avgidle 3 undertime 0
>>>
>>> ### bond0: traffic classes
>>>
>>> class cbq 1: root rate 2000Mbit (bounded,isolated) prio no-transmit
>>>  Sent 574330783 bytes 407225 pkt (dropped 2525, overlimits 0 requeues 0)
>>>  rate 0bit 0pps backlog 0b 0p requeues 0
>>>   borrowed 0 overactions 0 avgidle 3 undertime 0
>>> __________________________________________________________________
>>>
>>> I can't for the life if me work out why it is dropping so many packets 
>>> for while doing so little traffic when i enable  cbq the transfer rate 
>>> drops by approx 30%, any help would be great, and any improvements to my 
>>> command lines would be good also.
>>>
>>>
>>> Kingsley Foreman
>>>
>>
>>
>>
>>
> Could you provide your linux-2.6.25 .config file please ?
>
> What kind of hardware is your box ? (CPU, network interfaces)
>
> CBQ and other packet schedulers depend on a fast ktime_get() interface, so 
> maybe
> slowdown you notice has its root on core kernel facilities
> (CONFIG_HZ, SCHED_HRTICK, HIGH_RES_TIMERS, ...)
>
> If you remove CBQ, do you get same slowdown if you have a tcpdump running 
> on your machine ?
>
Im seeing it on a sun v20z and a sun x220m2, both multicore Opteron both tg3
Im not seeing a slowdown if tcpdump is running on the same machine without 
CBQ

you can grab the config here
http://games.internode.on.net/ker-config.txt