[Click] _iters_per_os in routerthread

[Eddie Kohler]

Ian,

What OS is this running on?  Are you using pcap?

Eddie


On 3/19/10 10:45 AM, Ian Rose wrote:
> 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
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