Re: [Xen-devel] [PATCH v3 1/3][xen-netback] add a pseudo pps rate limit

[Jian Wen <wenjianhn@xxxxxxxxx>]

AFAIK, TC doesn't support limiting packets per second.

2014-12-18 18:00 GMT+08:00 Sander Eikelenboom <linux@xxxxxxxxxxxxxx>:
>
> Thursday, December 18, 2014, 9:13:18 AM, you wrote:
>
>>>On Tue, 2013-07-09 at 16:01 +0200, William Dauchy wrote:
>>>> On Jul09 15:48, Sander Eikelenboom wrote:
>>>> > Just wondering, why should this be done in the drivers ?
>>>> > Couldn't this also be achieved with netfilter and the recent/limit 
>>>> > modules ?
>>>> > The limit module can already handle bursts.
>>>>
>>>> We indeed forgot to talk about it since we already got the question from
>>>> Wei.
>>>> The first thing is that your comment is also true for bandwidth which is
>>>> already present. Moreover PPS is linked to bandwidth.
>>>> By using netfilter, PPS shaping is done on backend level, once packet
>>>> has left the VM; which means after using an additional memory transaction
>>>> to copy packet from frontend. IMHO, at scale, shaping in this way should
>>>> save some memory transactions comparing to netfilter.
>>>
>>>Have you tried the netfilter approach and found it to be insufficient in
>>>practice?
>>>
>>>I'm not sure how netfilter recent/limit is implemented but if it queues
>>>rather than drops you would naturally find that you end up with back
>>>pressure onto the netback device where the ring would fill with
>>>in-progress requests and therefore netback would have to stop processing
>>>more packets.
>>>
>>>Ian.
>>>
>
>> The maximum limit rate of the netfilter limit module is 10000/s that is too
>>  small nowadays. Even if the size of the packet is 1500, the bandwidth is
>> as small as 14 MiB. So it is not a good practise to use the limit module.
>
>> $  sudo iptables -I INPUT -m limit --limit 10001/s --limit-burst 100 -j 
>> RETURN
>> iptables v1.4.19.1: Rate too fast "10001/s"
>
>
> And using TC / qdisc ? (http://lartc.org/manpages/tc.txt)
>



-- 
Best,

Jian

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