Java and Hyperthreading

Performance Tuning
#1

Hello,

I am about to order a dedicated server which has an Intel CPU with HyperThreading. I read a few rather disturbing reports about HT and Timers.

I am planning to run several game servers for my game on that computer. The servers use the GAGETimer to loop through the main thread.

Would intel HT screw up the timer? Does the OS matter in this regard, I was planning to go for a Fedora Linux system.

Should I opt for a slower non HT CPU instead?

Thank you,

KAding

#2

Quite possibly the hires timers will be buggered, yes.

Cas :slight_smile:

#3

So Cas is better able to answer the timign question.

Im just going to throw in the reminder that HT is pretty much functionally worthless SO if you can get a non HT CPU at the same or better clock speed for the same or less money, do that.

#4

My experiences with HT are that sometimes things are a bit faster, sometimes they’re a bit slower, and really it’s barely helped in the grand scheme of things… my real issues are with speedstep which has a far more drastic effect. Chances are though your CPU has speedstepping in it now.

BTW, this AMD64 Beast I won from the Sun compo. is just astounding.

Cas :slight_smile:

#5

Glad your enjoying the Opteron, you lucky stiff :slight_smile:

I don’t even have one for my lab yet :stuck_out_tongue:

#6

I recommend them :slight_smile:
Mmmm, dual core AMD64…

Cas :slight_smile:

#7

they are great!

#8

I have seen no evidence of HT affecting timing. It is useful for testing multi threaded code. Performance gains though are small.

#9

Actually Mark may be right there: HT may not be affecting timing; but all HT chips I’ve come across are also unfortunately afflicted with SpeedStep too which is the main culprit.

Cas :slight_smile:

#10

[quote]Actually Mark may be right there: HT may not be affecting timing; but all HT chips I’ve come across are also unfortunately afflicted with SpeedStep too which is the main culprit.
[/quote]
On notebooks? I tested timing on several desktops with HT cpus and never had a single problem.

#11

Is this a windows problem only? Or a particular versoin of speedstep?

I’ve got a speedstep laptop, and never had any major problems - except with linux itself - damn fool linux devs wrote a broken software clock that overwrites the hardware one (and doesn’t / didn’t get fixed for years).

For instance, the vast majority of games I’ve never had any timing problems; vaguely I recall I may have had a few rare occasions where timing was awry and no-one could work out why - but 99% of java games Just Work.

#12

We tell our customers to turn off hyperthreading. We found it destabilized the system (Win XP) in the same case where true dual processor machines remained stable.