[altq:1838] Re: [Q]about CBQ_MAX_CLASSES variable

[Kenjiro Cho <kjc@csl.sony.co.jp>]

soyoung@taonetworks.com
> Hi, I have a question about CBQ_MAX_CLASSES variable.
> 
> cbq_state_t structure has a 'cbq_class_tbl' member and it is allocated an 
> array of size 'CBQ_MAX_CLASSES' in the 'cbq_ifattach' function.
> Currently, CBQ_MAX_CLASSES is defined as 256 in the  'sys/altq/altq_cbq.h',
> and I think this variable shows the 'maximum number of effective simultaneous
> classes for the accuracy in bandwidth allocation' about altq mechanism..
> Am I right?
> 
> I need more classes for the CBQ configuration. According to the kernel code, 
> if I change the CBQ_MAX_CLASSES to the number greater than 256, 
> it doesn't seem to have any problem in compile, 
> but I'm not sure all those classes still show the same accuracy 
> about their allocated bandwidth. 
>
> I think if altq is run on the higher performance system, it doesn't affect
> the accuracy about bandwidth allocation to change CBQ_MAX_CLASSES. 
> Is there any recommendation or guide for setting CBQ_MAX_CLASSES variables?

It should be ok to increase CBQ_MAX_CLASSES.  (I've never tried it,
though.)

The algorithms used in ALTQ are not optimized for a large number of
classes.  But, as you said, today's CPUs are 10 times faster than
the CPU I used for developing altq-0.2 in 1997.  So, it won't be a
problem if you double or triple the number of classes.

-Kenjiro