device polling and weird timer interrupt count from vmstat

[Artem Kuchin]

Nikos Vassiliadis wrote:
> On Monday 24 September 2007 20:58, Artem Kuchin wrote:
>>> What i don't understand is why timer rate on each cpu is 1995? I
>>> have set it to 1000, not 1995 or 2000. I have seen it showing 2000
>>> on another box.
>>> So
>>> 1) why not 1000?
> 
> <DOUBLING>
> I can only make assumptions about the doubling, and I don't want to.
> FreeBSD is not a RTOS and some milliseconds variation is
> understandable. 
> 
>>> 2) if it is supposed to be doubled (why?) when why not 2000?
> 
> I can only make assumptions about the doubling, and I don't want to.
> FreeBSD is not a RTOS and some milliseconds variation is
> understandable. </DOUBLING>
> 
>>> 3) Is timer int really generated on each cpu?
> 
> Apparently, why do you doubt it?
> 
>>> Am i really wasting cpu
>>> time on ~4000 ints per second?
> 
> You can lower it you know, if you feel that you are waisting
> that much resources. Ofcourse you'll break your traffic flow
> that way, since latency will increase.
> 
> You seem very upset about it, are you sure you want to use
> polling(4)? it uses much more resources than interrupts.

I am not upset about all this. But i want to understand why is it
doubled. Because when i turn on polling i think that timer freq supposed
to be just like i set HZ. However, actually, i am now 
thinking about another issue.

I have dual CPU with HT. If i turn on HT (and it does help in my case)
it shoud 2000 int x4 = 8000 ints per second. SO, i have saved 200 int/second from
NIC and got myself 8000 ints/second from timer. Did i really win anything?
I wish there were some good explanation on this.

 
>>> 4) does twe driver use polling? whay about twa? how to check it in
>>> the sources?
> 
> Polling is only used on some network interface drivers. Polling(4)
> does not offer generic device-polling facilities.
> 
> By the way, you know your post has an aggressive sense, don't you?
> Please don't do this when asking questions and want replies.

Hmm.. Really? I didn't mean it, i was just trying to me as short and as
technical as possible. Alright, i'll give a though on how to be more..
polite, i guess.

--
Regards,
Artem