Re: [LARTC] How many (htb) tc classes and qdiscs are too many?

[Szymon Miotk <spam@crocom.com.pl>]

Spencer wrote:
> We have a Linux box that is acting as the gateway to the internet for about
> 400 people, typically there are not more then 50 of them using the internet
> at any given time.  We would like to provide different levels of access to
> different users.  For example 128kbps to some users and 256kbps to others.
> We have considered creating a class and qdisc for each user (using htb)
> however we don't know how much overhead creating 50-200 classes and
> qdiscs would involve, would this put too much strain on the Linux box?  Is
> it
> better to create fewer classes and qdisc and assign multiple users to each?
> I haven't been able to find any test on maximum effect number of qdiscs, but
> it could be I have just been looking in the wrong place.  If any one has any
> ideas or could point me in the right direction it would be greatly
> appreciated.

I have P4 3.0 GHz, 1 GB RAM.
I have 3500 potential users (top load about 800 users, average 400). I 
have 3 interfaces (2 WAN + 1 LAN), so I have 10500 queues total (3500 on 
each interface).
The traffic is 24Mbit max, average 20Mbit.

Without u32 hashing my box run at 60-70% CPU utilization. After applying 
hashing the box is running with 25% top utilization, average 15%.

The two thing you must remember when running a box for many users:
* use iptables chains. I prefer chains of 30-40 entries.
* use u32 hashing.
This will greatly improve CPU utilization. About 500-1000% in my case.

Szymon Miotk
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