Re: device polling and weird timer interrupt count from vmstat
- From: Oliver Fromme <olli@xxxxxxxxxxxxxxxxx>
- Date: Wed, 26 Sep 2007 17:00:57 +0200 (CEST)
Artem Kuchin wrote:
Well, problem with top is that on dual 3GHZ box it alsway s
shows 0% load when not loaded with real traffic (web traffic) no matter
if it is polling of int handling.
Great, so your machine doesn't have any significant overhead
for the timer interrupt. That was your question, wasn't it?
And when loaded with real traffic
web server eat a lot more cpu power then traffic handling, so, no
separate measurement of traffic cpu load is possible.
By "traffic cpu load" you mean the handling in the TCP/IP
stack and in the device driver, right? That's always the
same, no matter whether polling is enabled or not.
In fact, with polling enabled you get _less_ interrupts,
so the overhead caused by the actual interrupt handling
is smaller.
Also, when it comes to public web server i can never be secure enough and
crazy load of traffic can come any time from DDOS attack which can bring
down any box. So, for public web server it is a matter of security and
managebility to have server interactive even on high traffic load. So, even from
this poing of view polling can be usefull.
Not really. DDoS attacks against web servers usually work
on userland level, not on kernel level. For example, a
simple way to perform such an attack would be to make many
requests so that your apache runs out of resources.
Polling does not help at all in that case. Polling only
helps when the _kernel_ side is saturated with network
traffic, but that's usually not the case on a web server
where the Apache kicks the bucket much earlier than the
kernel.
Best regards
Oliver
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