Confused about Hyper-Threading: do you set it best to OFF as it can apparently decrease performance?!..

[Dance123]

Hi,

I am still very much confused about Hyper-threading and was wondering if it is best to turn it ON or OFF as apparently it can decrease performance.

In an older article you can read here they say "In the majority of cases, if you were to enable Hyper-Threading on a desktop PC you would not see a performance increase, rather a 0 - 10% decrease in performance."

Now, that doesn't sound good. Can I conclude from that that it's best to turn OFF hyper-threading. The article is from January 2002 with the 533Mhz P4 in mind I suppose, so I don't if this has changed now that you can buy 800Mhz FSB P4's or doesn't that make any difference.

Could anybody please clarify if it is best to turn HT ON or OFF when I will have my new 800Mhz Pentium 4 as this is all VERY confusing to me!! Does anybody understand all this! I thought HT was supposed to improve performance as so much hype has been around it and all I read are negative things about it?! I don't get it and all current P4s have HT ON by default if I am informed correctly!..

Thanks in advance to everybody who is capable of clarifying this. Why do all P4s have HT on now by default if it can decrease performance?!!..

 

[orion7144]

Leave it on. The bennefits outway any decrease (none noticed here). My benchmarks are similar on or off. However if I am using several programs I notice a big increase in performance.

 

[daveybrat]

I agree with Orion, my P4 does multi-task better with HT on..........However, I leave it disabled on my system
because it causes some of my older games to crash and it is a known issue with HT and older games.
Red Alert 2 is my favorite game and it only works with HT off. So if you don't play the older games you should
keep it on!

 

[dguy6789]

Keep it ON! The multitasking that hyper threading does is a great deal faster then mutli tasking with it off. hyper threading can increase performance by over 30% in some cases, if there is a performance decrease no way is it 10%, maybe 0.5 to 2%.

 

[Dance123]

Originally posted by: dguy6789
Keep it ON! The multitasking that hyper threading does is a great deal faster then mutli tasking with it off. hyper threading can increase performance by over 30% in some cases, if there is a performance decrease no way is it 10%, maybe 0.5 to 2%.

But in the article they say "In the majority of cases, if you were to enable Hyper-Threading on a desktop PC you would not see a performance increase, rather a 0 - 10% decrease in performance." That's exactly the opposite! Now I am completely confused! I would really appreciate it if somebody could clarify this once and for all!

Also, does HT work with ALL apps/games or only with apps/games especially written for it and will all other apps/games possible get a performance decrease when HT is on?!

 

[JeremiahTheGreat]

HT only works with multi-threading applications.

I think the moral of this whole thread is... turn it which ever you want, and be happy.

 

[Dance123]

Does HT also help when multi-tasking, ie. when you run multiple programs at the same time.

Also, what exactly are multi-threading apps and are there many of them, as I suppose this is something different then multi-tasking?

Oh, and what about the article mentioning a decrease of 10% in performance with HT on? When does that happen as they say that it happens in "the majority of cases" (see above)?

 

[Mark R]

HT only works with multi-threading applications.

The application will only run faster with HT if it is designed to have multiple threads. A multi-threaded program is one where more than one part of it can be running at the same time. Essentially, Windows will multi-task the threads, just as if they were seperate programs. For example, MS Excel uses 1 thread for dealing with displaying and editing your spreadsheet, and another thread for doing the calculations.

In a multi-CPU system the threads are divided between the CPUs so in the example above, while you are scrolling your spreadsheet, the window is being updated by 1 CPU, but the other CPU can do the spreadsheet calculations simultaneously. HT emulates a second CPU allowing a 2nd thread to use parts of the CPU that the 1st thread isn't using at that time.

However, don't forget that windows itself uses about 50 threads (just at idle), and that every program you are running, and every explorer window open all add another thread.

Even things like the 'file->open' dialog box is automatically given another thread by Windows.

With HT switched off, your application would have to stop while these tasks were processed. With HT switched on, all that happens is that your application *might* slow down while background tasks take place. In other words, you should notice that the computer in general is more responsive and multi-tasking smoother with HT switched on.

 

[dguy6789]

good example, but here it is in a simpler form.

With HT ON= you will be playing a game and you want to burn a cd in the background, it makes the game go not much slower at all.

with ht of= the game becomes almost unplayable when you try to burn cd at same time.

 

[ShortCappy]

HT also helps shave off about 7-9º C on a processor.

 

[rubix]

if you want to play an older game that doesn't work with hyper-threading on, like thief 1 and 2, use this program: http://pa-ftp.net4bay.com/tmp/PL/ProcessLoader.zip

 

[orion7144]

Originally posted by: Mark R

HT only works with multi-threading applications.

The application will only run faster with HT if it is designed to have multiple threads. A multi-threaded program is one where more than one part of it can be running at the same time. Essentially, Windows will multi-task the threads, just as if they were seperate programs. For example, MS Excel uses 1 thread for dealing with displaying and editing your spreadsheet, and another thread for doing the calculations.

In a multi-CPU system the threads are divided between the CPUs so in the example above, while you are scrolling your spreadsheet, the window is being updated by 1 CPU, but the other CPU can do the spreadsheet calculations simultaneously. HT emulates a second CPU allowing a 2nd thread to use parts of the CPU that the 1st thread isn't using at that time.

However, don't forget that windows itself uses about 50 threads (just at idle), and that every program you are running, and every explorer window open all add another thread.

Even things like the 'file->open' dialog box is automatically given another thread by Windows.

With HT switched off, your application would have to stop while these tasks were processed. With HT switched on, all that happens is that your application *might* slow down while background tasks take place. In other words, you should notice that the computer in general is more responsive and multi-tasking smoother with HT switched on.

This is a very good explanation.

Oh, and what about the article mentioning a decrease of 10% in performance with HT on? When does that happen as they say that it happens in "the majority of cases" (see above)?

That article was written back in Jan 02 so it is quite outdated.

 

[suklee]

Originally posted by: dguy6789
good example, but here it is in a simpler form.

With HT ON= you will be playing a game and you want to burn a cd in the background, it makes the game go not much slower at all.

with ht of= the game becomes almost unplayable when you try to burn cd at same time.

Wow , you actually can do this with HT?

How about office servers? I'm building a couple of office servers that'll be left on 24/7. Will end users really notice the difference between a 1.8A and 2.4C? One server will be used exclusively for E-mail (Exchange or Domino) and the other will just be a simple PDC/file archive unit. I guess with a difference of only ~US$ 50, it would not make sense for me not to go for the 2.4C?

 

[orion7144]

Originally posted by: Kai920

Originally posted by: dguy6789
good example, but here it is in a simpler form.

With HT ON= you will be playing a game and you want to burn a cd in the background, it makes the game go not much slower at all.

with ht of= the game becomes almost unplayable when you try to burn cd at same time.

Wow , you actually can do this with HT?

How about office servers? I'm building a couple of office servers that'll be left on 24/7. Will end users really notice the difference between a 1.8A and 2.4C? One server will be used exclusively for E-mail (Exchange or Domino) and the other will just be a simple PDC/file archive unit. I guess with a difference of only ~US$ 50, it would not make sense for me not to go for the 2.4C?

Exactly

 

[suklee]

Muchos gracias senor

 

[Dance123]

Originally posted by: ShortCappy
HT also helps shave off about 7-9º C on a processor.

Isn't it the opposite, meaning that with Hyper-Threading ON the CPU runs around 5°C HOTTER or am I wrong about this?

 

[batmang]

i love being able to burn cd's and play a game at the same tmie and not have it coaster. i love hyper threading, leave that shiz on

 

[RedDog75]

I am a convinced man! I have been desperately trying to figure out why my CPU at one point was running at around 43C idle and all of a sudden, I had a computer running close to 53-54C!!! (Little did I know at the time that it had a lot to do with my disabling HT in BIOS, 'cause I read boards saying how it decreases performance) I have been posting the Cooling help boards on this site for someone to help! As I just about had it with frustration, just out of curiosity I was looking for a new case and I found that someone on Newegg had posted approx a 10degree difference with Hyperthreading enabled. So I tried it myself. WHOA!!! I don't care what anyone says about this computer not running efficiently with Win2K and HT! I noticed both a performance increase AND a temp decrease!

I say forget what Intel and Microsoft say - go for it! It is well worth it.

 

[Wingznut]

Originally posted by: orion7144

Oh, and what about the article mentioning a decrease of 10% in performance with HT on? When does that happen as they say that it happens in "the majority of cases" (see above)?

That article was written back in Jan 02 so it is quite outdated.

There's your answer... You are looking at an old article. Intel has changed the HT just a bit for the desktop processors.

Take a look at this more recent article and see what I mean.

And here are some multitasking benchmarks.

Originally posted by: RedDog75
I say forget what Intel and Microsoft say - go for it! It is well worth it.

Last time I checked, Intel and MS really like HT and neither one suggests turning it off.

 

[WarpSpeed]

Running Win2K with SP4. I get better video benchmarks and significantly improved SuperPi results with HT disabled. However, if I run three instances of video encoding similtaneously, I see greatly improved performance with HT enabled. I recognize that XP probably makes more efficient use of hyperthreading. You should do your own comparisons, using your computer the way you mostly do.

 

[dullard]

Originally posted by: Dance123
Hi,

I am still very much confused about Hyper-threading and was wondering if it is best to turn it ON or OFF as apparently it can decrease performance.

In an older article you can read here they say "In the majority of cases, if you were to enable Hyper-Threading on a desktop PC you would not see a performance increase, rather a 0 - 10% decrease in performance."

Now, that doesn't sound good. Can I conclude from that that it's best to turn OFF hyper-threading. The article is from January 2002 with the 533Mhz P4 in mind I suppose, so I don't if this has changed now that you can buy 800Mhz FSB P4's or doesn't that make any difference.

Could anybody please clarify if it is best to turn HT ON or OFF when I will have my new 800Mhz Pentium 4 as this is all VERY confusing to me!! Does anybody understand all this! I thought HT was supposed to improve performance as so much hype has been around it and all I read are negative things about it?! I don't get it and all current P4s have HT ON by default if I am informed correctly!..

Thanks in advance to everybody who is capable of clarifying this. Why do all P4s have HT on now by default if it can decrease performance?!!..

Essentially there are several issues to consider.
1) That article is on early Xeon models, not P4s.
2) Hyperthreading has been significantly improved since that time - and it will be improved again with the new Prescot processor.
3) Win 2k for some reason tends to dislike hyperthreading (as will other OS made before HT was around).
4) Programs weren't aware of HT back then, and thus couldn't be programed to take advantage of it.
5) HT can only get better as processor speeds increase (we are at 3.2 GHz now and when that article was written we were at 2.0 GHz).

So take a new P4 with Win XP and you will see a performance gain or at least equal performance in the vast, vast majority of single programs. There is the rare exception where there is a mild decrease (like 1%) but you'll never see it. However when you do multiple things at once - the difference is night and day better with HT. For example you are playing a game and your virus scanner kicks in (HT turned on is so much better in this case).

 

[Mickey21]

It's not like you need a team of people working night and day to figure this out, just try it yourself. That's always the way to approach a problem like this. Run some of the things you do with it on, and then run them with it off. See which one you like better and run with it. Things may play out differently for your particular setup. Personally, I say leave it on. But that's my setup and my set of applications.

 

[Dance123]

Regarding temperature, are you sure that when HT is ON that temperature DECREASES compared to when HT is OFF?! I thought I read once that HT INCREASED CPU temperature because of the multi-threading going on which demands more from the CPU at the same time or something, but I am no expert so I might be completely wrong about this.

Anybody can clarify this please in order to avoid any confusion about this?! Thanks!

 

[AndyHui]

Temperature increases when HyperThreading is enabled and run with an OS that fully supports HT.

More of the CPU die is in use, resulting in greater heat output.

 

[Accord99]

However, when a HT computer is idle or near-idle, evidence suggests that the CPU temperature is significantly reduced as compared to when in non-HT mode.
See here: http://www.xbitlabs.com/articles/cpu/display/p4-temp.html
About 2/3rds of the way down. In fact, in most cases the HT processor is a bit cooler.

One possible explanation is that XP features a more aggressive use of HALT instructions with HT processors, but I'm not sure it would have resulted in 8 degrees difference at idle.