[Linux-PowerEdge] Intel's Hyper-Threading vs. Linux Iptables/Netfilter Firewall ?

Dan Pritts danno at umich.edu
Wed Mar 20 08:36:01 CDT 2013

>     I've been doing some research and couldn't find anything relevant
>     regarding
>     my question. All I got so far was people saying things like :
>     - " you should enable Intel's HT on a web server "
> I don't see any reason not to enable HT.
I agree with you that I would turn on HT unless I had a reason not to.

However, I can imagine HT hurting performance overall if it ends up 
causing the CPU caches to be overloaded.

>     I also read this (
>     http://i.dell.com/sites/content/shared-content/data-sheets/en/Documents/configuring-low-latency-environments-on-dell-poweredge-12g-servers.pdf)
>     from Dell. They simply say the recommended setting for "logical
>     processor"
>     (Intel's HT) is "disabled", but don't tell anything more... Why do
>     they say
>     that ?
> I don't see the word hyperthreading or letters HT in that document.
> I see disabling Virtualization Technology is mentioned though.

It mentions "Logical Processor" which is indeed hyperthreading.  I can 
imagine that It may make sense to disable HT if you want to ensure that 
high priority jobs get full use of their CPU core.

I don't know that the absolute lowest latency is the goal with a 
firewall, though, at least not under a Denial of Service attack.  
Dealing with DoS is very parallelizable.

> - have a good look at the NICs you use and the drivers that go with 
> it. And possibly upgrade the kernel to a newer version to get better 
> performance. I guess the default onboard NIC is the Broadcom Xtreme II 
> ? If I understand correctly you probably want Intel NICs, they have 
> multiple queues which means interrupts and packets can be devided over 
> different cores.

Intel server NICs are great, and are likely better than whatever is on 
the motherboard.  There are other good NICs out there; don't buy an 
Intel "desktop" NIC.

The real answer to the original question:  try it both ways.
Dan Pritts
ICPSR Computing & Network Services
University of Michigan
+1 (734)615-7362
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