Hyper-threading on or off?

[Catsrules]

I just got a used server to play around with and I was wondering if I want Hyper-threading on or off? I don't know the exact specs on the CPUs just they are intel Xeon and 3.4Ghz. I think it is just a big brother to the Pentium 4.

 

[hunter315]

There are a great many Xeon chips, they are Intel's server line up. Download an run CPU-Z it will tell you exactly which Xeon you have and if it has hyperthreading or not.

 

[sk1n5]

On. What hyperthreading does is allow one physical processor to handle 2 threads simultaneously. What this means is that when the CPU finishes its work for the current clock cycle, if it does it in a quarter of the cycle it sits idle for the remainder of that cycle. Hyperthreading allows it to fill that space with another task, thus that core is performing two tasks in one clock cycle. This is a particularly helpful feature if you plan on using this server as a file server, since the server will be handling many small tasks at once.

 

[Catsrules]

On. What hyperthreading does is allow one physical processor to handle 2 threads simultaneously. What this means is that when the CPU finishes its work for the current clock cycle, if it does it in a quarter of the cycle it sits idle for the remainder of that cycle. Hyperthreading allows it to fill that space with another task, thus that core is performing two tasks in one clock cycle. This is a particularly helpful feature if you plan on using this server as a file server, since the server will be handling many small tasks at once.

Ok I will turn it on then, since I will be useing this as a file server. I have heard the Hyperthreading hurts performance when you do certain tasks. And it was turned off when i got the server so I was wondering it there was a reason it was off.

 

[sk1n5]

The only reason I can think of is power savings. Having hyperthreading turned on consumes a little more power and makes the processor run a little hotter. Nothing major, but a thought.

 

[hunter315]

On XP or older versions of windows there was a chance that a single thread would get dropped into the logical hyper threading core not into the main physical core so it would suffer reduced performance. Core management in windows has improved since then so the performance difference you will see is almost none in tasks with low thread counts, in multi threaded tasks it can significantly boost performance. The difference in power consumption will be pretty minimal so i wouldnt worry about that.

 

[king smp]

This is a link to an old THG article that does one of the best jobs of explaining HT.
http://www.tomshardware.com/reviews/intel,557.html
Hyperthreading has improved since that article.
The Prescott series P4 intro'd HT2 than later Xeons utilized cache queing which reduced cache thrashing and made HT even better.
The way software is written currently you are definitely better off w/ HT on.
In the beginning in 2002 some apps would suffer due to HT but that is not true of newer better written software.
In a single threaded app you will not see a performance gain but as already stated you will be able to run other apps at same time more efficiently.
Early HT paved the way for better written software for multi-core systems today.

 

[Catsrules]

Best answer selected by Catsrules.

 

[Mousemonkey]

This topic has been closed by Mousemonkey