[Click] _iters_per_os in routerthread

[Ian Rose]

Hi Eddie,

I'd be more than glad to send along my "real" config, but its really big 
and uses quite a lot of custom elements that won't mean anything to you 
without the source code.

However, just for testing these changes I used:

FromDevice(ath1, ENCAP 802_11_RADIO, PROMISC true, HEADROOM 196) -> Discard;

I am seeing about a 2x CPU usage difference when I use _iters_per_os = 2 
vs 64.

- Ian


Eddie Kohler wrote:
> Hi Ian,
> 
> (1) I would completely appreciate seeing your config, just to see if 
> there's anything that might cause the extra CPU usage.  BUT:
> 
> (2) _iters_per_os is set that way just, I think, as a random guess.  ANd 
> that guess is at least 5 years old and probably more.  I think it would 
> be OK to set it to 2 for everyone.
> 
> Eddie
> 
> 
> On 3/18/10 8:06 PM, Ian Rose wrote:
>> 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
>> _______________________________________________
>> click mailing list
>> click at amsterdam.lcs.mit.edu
>> https://amsterdam.lcs.mit.edu/mailman/listinfo/click