bfifo limit explanation

Hi there,

I'm wondering If someone can clarify some pfifo-bfifo questions

So, pfifo use packets and its limit defaults to txqueuelen and bfifo is 
txqueuelen multiplied by the interface mtu, default txqueuelen is 1000 
on my machine

But what if I play around with this and set a txqueuelen to a gigantic 
value like 10000 but set the bfifo limit to my bandwidth*delay product, 
upon congestion what will happen? I assume the bfifo will limit the 
queue to the value I want but will this interfere with the interface 
queue length?

My plan is setting bfifo limit in my interface to the bdp assuming 100ms 
of delay

So with an egress of 50mbit and assuming 100ms delay I have a bdp of 
625000, if I set this as bfifo limit, this means that the queue can hold 
up to 100ms of data?

Is this a correct thing to do? Does that make sense?

Also, I noticed that in my machine (Debian 11, Kernel 5.10) I have 
access to pfifo_head_drop but there is no bfifo_head_drop, why is that?

thanks.