To HT or not to HT, that is the question

[Toff]

Hi,

I've used HT for a while on my 3.0 P4 - I like the way it helps you multi-task better by not letting one program nick all of the CPU power.

It's especially useful when one program crashes - it can only max-out one half of the CPU (if you've set the affinity correctly).

That's great, but is it counter-productive on an overclocked system? If you've raised the FSB to increase the CPU speed, by 400MHz (for example) your programs will only see a 200MHz boost (unless they are designed for HT / multiprocessor - which none of mine are!)

What are people's thoughts on this? Is it best to turn the HT off so your programs / the OS can enjoy the fruits of your overclocking? Do I have the wrong end of the stick?

- Toff.

 

[Toff]

No, if you raise the FSB to run the CPU at 3.4GHz, it runs at 3.4Ghz. You get the 400MHz boost all the time.

But with HT, if you are encoding an MPEG to AVI for example (which I regularly do to get movies onto my Archos) it will max-out one side of the processor whilst the other side remains idle (see below for an example).

To me, that means the application isn't making use of the processor's capabilities or the extra MHz you're freed-up by over clocking. I wonder if the same would Apply to the OS itself (or would it use the processor more intelligently?)

- Toff.

 

[Toff]

Thats just a 'windows' issue.

Windows is thinking you have 2 fully working processors. In reality you have a single processor which can do 125% cpu load.

Cheers for your explanation.. I posted the performance monitor pic at the same time you posted (hadn't seen your reply)... I now understand, many thanks

That settles it - I'll leave it HT

- Toff.

 

[Toff]

Average joes shouldn't really be digging this deep into their system. Nor should anybody be using the "Set Affinity" option for anything other than compatibility reasons.

Who 'choo callin' an "average Joe" fool?

I set the affinity, because one of the programs I use, occasionally crashes (despite being at the latest revision etc).

If I un-tick the affinity for the second CPU (HT virtual CPU obviously) for that process; when it crashes, I'm still able to navigate to the Task Manager and end the process.
If the process is active on both affinities when it crashes, the computer runs to slowly to do anything (5 mins for Task Manager to open) and I have to re-boot.

Setting the affinity on the Multi-processor servers at work is a very valuable tool - you can dedicate an entire PC to Exchange's store process (for example) which we've seen performance gains from.

- Toff.

 

[Toff]

Who 'choo callin' an "average Joe" fool?

I set the affinity, because one of the programs I use, occasionally crashes (despite being at the latest revision etc).

If I un-tick the affinity for the second CPU (HT virtual CPU obviously) for that process; when it crashes, I'm still able to navigate to the Task Manager and end the process.
If the process is active on both affinities when it crashes, the computer runs to slowly to do anything (5 mins for Task Manager to open) and I have to re-boot.

Setting the affinity on the Multi-processor servers at work is a very valuable tool - you can dedicate an entire PC to Exchange's store process (for example) which we've seen performance gains from.

- Toff.