Limit-at and Max-limit

fernando143 · Tue Aug 21, 2018 11:54 pm

Hi, I 'm confuse with limit-at and max-limit.

For example, if I have got a parent download with max-limit 5M
and two children queue, both with max-limit 5M. It's okey?
Or maybe it should be max-limit 2.5M for both?

I read that the sum of all the max-limit of thechildren queues should not be greater than the max-limit of the parent queue. It's wrong or it's okey? for example

0   name="Downsteam-ISP" parent=bridge1 packet-mark="" limit-at=0 queue=pcq-download-default priority=8 max-limit=1900k 
     burst-limit=0 burst-threshold=0 burst-time=0s bucket-size=0.1 

 1   name="Upsteam-ISP" parent=Wan packet-mark="" limit-at=0 queue=pcq-upload-default priority=8 max-limit=350k burst-limit=0 
     burst-threshold=0 burst-time=0s bucket-size=0.1 

 2   name="lol_up" parent=Upsteam-ISP packet-mark=LOL_PACKET limit-at=100k queue=UP priority=1 max-limit=350k burst-limit=0 
     burst-threshold=0 burst-time=0s bucket-size=0.1 

 3   name="lol_down" parent=Downsteam-ISP packet-mark=LOL_PACKET limit-at=190k queue=DOWN priority=1 max-limit=1900k 
     burst-limit=0 burst-threshold=0 burst-time=0s bucket-size=0.1 

 4   name="other_down" parent=Downsteam-ISP packet-mark=OTHERS_PACKET limit-at=1M queue=DOWN priority=6 max-limit=1900k 
     burst-limit=0 burst-threshold=0 burst-time=0s bucket-size=0.1 

 5   name="other_up" parent=Upsteam-ISP packet-mark=OTHERS_PACKET limit-at=200k queue=UP priority=6 max-limit=350k 
     burst-limit=0 burst-threshold=0 burst-time=0s bucket-size=0.1 

 6   name="icmp_down" parent=Downsteam-ISP packet-mark=ICMP_PACKET limit-at=2k queue=DOWN priority=1 max-limit=1900k 
     burst-limit=0 burst-threshold=0 burst-time=0s bucket-size=0.1 

 7   name="icmp_up" parent=Upsteam-ISP packet-mark=ICMP_PACKET limit-at=2k queue=UP priority=1 max-limit=350k burst-limit=0 
     burst-threshold=0 burst-time=0s bucket-size=0.1 

 8   name="mega_down" parent=Downsteam-ISP packet-mark=MEGA_DOWN_PACKET limit-at=300k queue=DOWN priority=8 max-limit=1900k 
     burst-limit=0 burst-threshold=0 burst-time=0s bucket-size=0.1 

 9   name="mega_up" parent=Upsteam-ISP packet-mark=MEGA_DOWN_PACKET limit-at=40k queue=UP priority=8 max-limit=350k 
     burst-limit=0 burst-threshold=0 burst-time=0s bucket-size=0.1 

10   name="dns_down" parent=Downsteam-ISP packet-mark=DNS_PACKET limit-at=8k queue=DOWN priority=1 max-limit=1900k 
     burst-limit=0 burst-threshold=0 burst-time=0s bucket-size=0.1 

11   name="dns_up" parent=Upsteam-ISP packet-mark=DNS_PACKET limit-at=8k queue=UP priority=1 max-limit=350k burst-limit=0 
     burst-threshold=0 burst-time=0s bucket-size=0.1

The code above it's oke? or the sum of all max-limit of queue children should be lower o equal than max-limit of the parent?

xvo · Wed Aug 22, 2018 12:25 am

The max-limit of all children queues has to be lower than max-limit of their parent.
A little lower is enough.
If only one of the children is active it is ok if it takes the whole bandwidth allocated for parent.
But the more "spare" bandwidth you have for the parent max-limit over the children's max-limits, the higher the chance that no packets are dropped, in case the traffic increases instantly.

The sum of limit-at for children has to be lower or equal to max-limit of the parent:
limit-at is a kind of "guaranteed bandwidth", so it makes sense, that you can only guarantee something for all the children queues at once only when the sum of guaranteed bandwidth for them is lower than you allow the parent queue to have.

fernando143 · Wed Aug 22, 2018 12:44 am

so, if I understood good, I should be it:
Parent max-limit 5M
children1 limit-at 2.4M max-limit 5M
children2 limit-at 2.4M max-limit 5M

It's okey?

xvo · Wed Aug 22, 2018 1:32 am

I would add a little more overhead, especially for limit-at (you are not really cutting anything):

Parent max-limit 5M
children1 limit-at 2M max-limit 4.5M
children2 limit-at 2M max-limit 4.5M

You can try different values trying to minimise the number of packets dropped.

BTW, you can set different priority for children: the lower the number, the higher the chance that this child will get bandwidth over its limit-at.
If in my example child1 has priority 1, and child2 has priority 8 and both are trying to max out:
child2 will get bandwidth according his limit at - 2M
child1 will get 2M + 1M (the rest of paren's max-limit)
Or something close to this.
I guess if the priorities will be closer to each other they will share 1M in some proportion in favour of the child with higher priority (lower priority number).

Limit-at and Max-limit

Limit-at and Max-limit

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