[Click] _iters_per_os in routerthread

[Ian Rose]

Hi all -

In lib/routerthread.cc there is the following code:

#if CLICK_USERLEVEL
     _iters_per_os = 64;           /* iterations per select() */
#else
     _iters_per_os = 2;          /* iterations per OS schedule() */
#endif

I'm curious if there is a particular rationale behind the value 64 for 
userlevel click.  Is it simply the case that this value works pretty 
well for most of the typical click configurations that were tested?  In 
my (admittedly brief) testing, it appears that this parameter choice 
imposes a CPU overhead of ~3x for [some?] select-heavy applications, by 
which I mean configs that spend most of their time calling selected() on 
elements, rather executing tasks or timers.  For example, my particular 
app uses around 15-20% CPU with the above values, but if I change the 64 
to a 2, the CPU usage drops to 5-6%.

Obviously this might simply be a case of the default parameters not 
being particularly good for my specific situation, but I thought I'd 
check since the performance difference seemed pretty significant.

cheers,
- Ian