[Click] _iters_per_os in routerthread

[Ian Rose]

Sorry yeah should have specified that - I forgot that FromDevice is 
different on Linux.

I am on FreeBSD 7.2-STABLE.

Also, I am using Click v1.7.0rc1, but I compared FromDevice.u and the 
relevant portions of routerthread.cc to HEAD and didn't see anything 
different.

- Ian

Eddie Kohler wrote:
> 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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