Re: [LARTC] various questions about tc & htb

[Stef Coene <stef.coene@docum.org>]

> You don't have to, but HTB assumes a mtu of 1600 by default which is
>
> a) wrong in most cases
> b) not always the same (e.g. loopback default is 16436)
>
> ------------< snip <------< snip <------< snip <------------
> root@oasis:~# tc class add dev eth0 parent 1:1 htb help
> Usage: ... qdisc add ... htb [default N] [r2q N]
>  default  minor id of class to which unclassified packets are sent {0}
>  r2q      DRR quantums are computed as rate in Bps/r2q {10}
>  debug    string of 16 numbers each 0-3 {0}
>
> ... class add ... htb rate R1 burst B1 [prio P] [slot S] [pslot PS]
>                       [ceil R2] [cburst B2] [mtu MTU] [quantum Q]
>  rate     rate allocated to this class (class can still borrow)
>  burst    max bytes burst which can be accumulated during idle period
> {computed}
>  ceil     definite upper class rate (no borrows) {rate}
>  cburst   burst but for ceil {computed}
>  mtu      max packet size we create rate map for {1600}
>  prio     priority of leaf; lower are served first {0}
>  quantum  how much bytes to serve from leaf at once {use r2q}
>
> TC HTB version 3.3
> root@oasis:~#
> ------------< snip <------< snip <------< snip <------------
>
> See, mtu = 1600 by default.
I did a quick search in the source of iproute2 and kernel, and as for as I can 
see is mtu used to calculate the minimal burst :
        /* compute minimal allowed burst from rate; mtu is added here to make
           sute that buffer is larger than mtu and to have some safeguard 
space */
        if (!buffer) buffer = opt.rate.rate / HZ + mtu;
        if (!cbuffer) cbuffer = opt.ceil.rate / HZ + mtu;

Stef

-- 

stef.coene@docum.org
 "Using Linux as bandwidth manager"
     http://www.docum.org/
     #lartc @ irc.oftc.net

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