HT: enable or disable?

[CheeZeTM]

What are the benifits of Hyper Threading?
Dissadvantages?

i know that it makes your pc "think" it has 2 cpu's, also for programs that suck up alot of CPU it will only suck up half of it

[Jiggahurtz]

Anybody who thinks that with HT on means only half of your cpu is getting used by a program that doesn't support smp is quite simple minded in my opinion. HT simply allows your processor to hand 2 tasks at once that require different parts of the cpu. It makes switching between two heavy cpu usage proggies much more smoothly. In that sense then yes each thread gets 50% of the cpu time but they switch much more quickly than on a HT disable P4. Basically there are no disadvantages to HT that I know of. Its a good thing that should be left on. Just like L2 cache on a cpu.

[Lat]

left on.
there's no disadvantages at all, like already iterated

[CheeZeTM]

OK so lemme re-phrase what i think, your PC fuctions as a dual processor board, if a program needs 100%CPU to run no matter how fast the CPU is it has to have all of it, only one of the HT enable parts of the processor is used or 50% of the avalible useage still allowing other programs to use the other half

[SLee]

OK so lemme re-phrase what i think, your PC fuctions as a dual processor board, if a program needs 100%CPU to run no matter how fast the CPU is it has to have all of it, only one of the HT enable parts of the processor is used or 50% of the avalible useage still allowing other programs to use the other half
No, if you are running only a single threaded program, when Task Manager says 50%, it is in fact running as fast as the single thread can possibly go. There is nothing being held back in reserve. However, when you run two threads or applications, then certain portions of the P4 is split in half and instructions from both threads can be executed simultaneously. In general, this results in 10-30% gain in throughput.

[CheeZeTM]

arg, i dont know how to put what i think into words, there are 2 threads in a Ht enabled processor correct? if so then (in my case) Windows thinks there are 2 processors, each at 3.1(in my case) or is each read as 1.55?(hardware monitor says 3.1)

[SLee]

arg, i dont know how to put what i think into words, there are 2 threads in a Ht enabled processor correct? if so then (in my case) Windows thinks there are 2 processors, each at 3.1(in my case) or is each read as 1.55?(hardware monitor says 3.1)
When you're running a single-threaded application, the logical processor where the app is running is running at fullspeed, 3.1GHz in your case. With two threads or apps, each app gets about half of the CPU resources but due to HT, each app runs typically between 55% to 65% (depends on the app) compared to running the app by itself. On non-HT processors, running two CPU intensive apps usually results in each app running at 50% as compared to running one app by itself.

[hUMANbEATbOX]

Anybody who thinks that with HT on means only half of your cpu is getting used by a program that doesn't support smp is quite simple minded in my opinion.

simple minded is harsh, he just didn't know. you weren't born with a vast array of knowledge, so relax.

[CheeZeTM]

OK i understand now, and i was wrong on my thoughts, so basicly HT is sort of like overclocking correct?

[CheeZeTM]

Thankyou Mr. Beat Box, you bring back classroom memory's of our "human beat box" in my vocational computer/electronics class, the other kids had to do something while i was doing all the work

[SLee]

OK i understand now, and i was wrong on my thoughts, so basicly HT is sort of like overclocking correct?
Well I wouldn't say its overclocking but it has the same benefits of a dynamic overclocking feature that increases the CPU clock by 10-30% whenever you have two or more CPU intensive threads or applications running simultaneously.

[Randyman...]

Ancient thread bump. Isn't the Search function grand :)

So, I have an application that only uses 50% of the CPU with HT engaged. Would this application run any faster w/o HT engaged? The application in question is an Audio Application called "Nuendo" (supposed to be multi-threaded, but I have some doubts TBH), and this is the dedicated application this PC uses (it is a Digital Audio Workstation - PC#2 in my Sig). I'm NOT multitasking with this PC - it has a dedcated purpose: Audio Production. I'm trying to get my I/O Latency down as low as possible.

I'd like to test this for myself, which leads to another Q: Can I disable HT w/o re-installing XP? And then re-enable HT? Might this trigger XP product activation? (Same MAC address - so I wouldn't think so).

I was always under the impression that a single threaded app could NOT utilize all of a HT CPU's resources (like a single instance of "Super Pi" for instance). Is this incorrect?

Thanks for your thoughts :cool:

[hUMANbEATbOX]

Ancient thread bump. Isn't the Search function grand :)

So, I have an application that only uses 50% of the CPU with HT engaged. Would this application run any faster w/o HT engaged? The application in question is an Audio Application called "Nuendo" (supposed to be multi-threaded, but I have some doubts TBH), and this is the dedicated application this PC uses (it is a Digital Audio Workstation - PC#2 in my Sig). I'm NOT multitasking with this PC - it has a dedcated purpose: Audio Production. I'm trying to get my I/O Latency down as low as possible.

I'd like to test this for myself, which leads to another Q: Can I disable HT w/o re-installing XP? And then re-enable HT? Might this trigger XP product activation? (Same MAC address - so I wouldn't think so).

I was always under the impression that a single threaded app could NOT utilize all of a HT CPU's resources (like a single instance of "Super Pi" for instance). Is this incorrect?

Thanks for your thoughts :cool:

windows says that only 50% is being used, because windows truly believes that there are 2 real cpu's in your system. when running a single threaded app, 50% really means 100% (well, close, 99%ish).

turning off HT will most likely not affect your I/O latency in the least. i would think this would be more bound to the quality of your soundcard.

you can turn off HT with no ill effects to your XP install. you do it in the bios, its as simple as setting and rebooting.

a single threaded app can use virtually all resources. running superpi with HT off may yield very minimal gains. like, if you can run a 1m in 35.000s with your 4ghz p4, you may drop it to 34.950s. it is really insignificant.

but hey, test it and see for yourself. ;)

p.s. thanks for the conscious ancient thread bump. most times, when people bump old threads, they try to pick up the conversation right where it left off, totally unaware of what year it is. :D

[Randyman...]

Thanks for the speedy reply. And, yes - I also find it odd to revive a thread from years ago as if it was current yesterday :) .

That makes more sense, and falls in line with the rest of this thread. I'll probably skip the HT tinkering. I think this rig is about to die anyway. I had to smack it to get it to POST the other day :eek: . A C2D is in my near future, and my current Presler system (PC#1 in sig) will replace this 4GHz P4 system soon.

PS - Soundcard is RME HDSP Digiface or Multiface (I have 2 of each ;) ). I love having the same soundcard in all 3 of my DAWS - then I can use whichever rack of gear I need (the Digiface/Multiface breakout boxes live in the equpiment racks, but the PCI cards obviously stay in the PC's). Easy swapping, and my Audio Application doesn't even know I swapped interfaces!

:cool:

[hUMANbEATbOX]

hey no probs..

sounds like you've got a pretty sweet setup. ;)

i like to play with making music on my rig. i've got reason 2.5, and i use that quite a bit. basically just put together simple tracks for friends to exploit later on. my Audigy (original) is still serving my purposes, but my needs are fairly simple (you don't need 100 tracks at once to make a nice funky beat ;))