Hyperthreading - is it a big deal?

[Jeff7181]

Originally posted by: Duvie
Jeff...really I was running 2 monitors and I would run a movie on the LCD while I was working (cad) on the CRT...while downloading music files....Folding in the background or converting 1 of my 50+ Divx files to DVD format.....System was very responsive and all things were working well and getting work done....system was pegged at 100% load all the time (2 x 50)....

One could do a lot, especially when at the time I may have only had about 3-4 hours on the PC....I needed to get rid of those damn 100+ cd-rom disc...

I have no doubt you did... 4 applications running is not uncommon... hell I have Trillian running, Steam, Firefox with 4 tabs open, Thunderbird, WMP10 (playing ~256kbps VBR wma's), MS Word, Motherboard Monitor, and Prime 95 running and it's no less responsive than if I just had Firefox open.

 

[Duvie]

problem is, it is not about the number of programs opened and windows opened. It is about cpu intensive apps running...Now prime is cpu intensive but it is default low priority so everything will take from the cpu cycles first...what is left??? Nothing you really listed is going to command a whole helluva a lot by itself let alone adding them up....

not apples and apples here.....

Working for me in cad means rendering 20-30 sec walk thrus 15-30fps.....the dvd movie was only like 15-20% max...rendering would try to take 100%, and when TMPGenc was going it didn't take low priority and would take about half the power....would take 100% of both virtual cpus if it could by itself....same with the viz renderer

This is about cpu intensive apps....about cpu intensive apps that are not low priority background apps....I added FH as an example because on the P4 system it will get work done oin both thanks to the HT....I can attest this absolutely does not happen on the AMD system.....Anyone who says it does is not running another cpu intensive app or is a liar....


Right now....

TMPGenc.... Csi epsiode (Xvid) to DVD....100% cpu usage....FH running...in the last hour!! Not one bit of movemet or more precenatge complete on the FH work unit.....

On the P4 system I would get about 80-85% the tmpgenc performance (which would be about equal to what my 100% A64 performance is now) but I would in this hour probably have gotten 25%-30% done from what I would have normally if it was the only app running....


This is HT at its best....2 apps is all that is needed....where ppl add the additional ones is trying to say the system doesn't lag....That is the crock of it...The AMD system does not lag either...it switches priorities around and makes things work. NO additoinal work is done. FH will still get nothing and any other app if in the foreground will just steal from the TMPGenc program and slow it down....


2 instance of FH running simultaneously can usualy garner me about 30-35% additional work being done versus 1 instance....

I ran the SETI here back early last year and 2 instances of seti ran up to 40% faster....

1 unit was done in 2 hrs 4min and 2 units were done in 2hr 59mins for 1 per 1hr 29min

 

[Wedge1]

Thanks for the responses in this thread. The OP asked for some answers from guys that have had the chance to really compare the two. He never said he wanted anything scientific, so keep it coming if you have something to share.

I'm interested in HT as well. Specifically, I have wondered how it affects multi-tasking. Does it create good response time to commands when several apps might be running? And I think the answer to that is 'yes' since a few of of you described it as "hiding latency".

I personally will never try to play a game and encode video at the same time. Both would do best to have all the resources available to them. But realistically, I will have Outlook Express opened, MS Word, Nero will be burning a cd, and music will be playing all while I have a few internet pages opened. So for this, it sounds like HT is the way to go.



EDIT: I just read Duvie's last post. I think he is disagreeing with the "no-lag-during-multi-tasking" concept but instead is saying that HyperThreading handles CPU-intensive tasks better than an AMD 64 would?

 

[jbh129]

The most noticeable HT benefit I see with my 2.8c when compared to my 3200+ winnie at 2.7 is that when Norton scans for viruses, I can still watch a movie or encode a movie. Norton cripples my AMD rig. I bought my AMD rig as an experiment in overclocking and while I have gotten lower superpi times and higher 3dmark scores, the upgrade was negligible at best. Thats why my Intel became an HTPC. I like being able to rip 1 movie and watch another at the same time.

 

[Wedge1]

Guys I have a question about enabling/disabling hyperthreading. I have read elsewhere (erroneously perhaps, not sure) that enabling hyperthreading in the BIOS will not work unless you install the operating system AFTER enabling it. Same would go for disabling, i.e., changing it means re-installing the OS for the change to take effect. Or, said conversely, have it at the appropriate setting before installing the operating system in order for it to work.

Is this true or is it rubbish?

 

[Conky]

For what it's worth, I find hyperthreading to be a very useful thing. I have a Northwood 3.06 P4 and am quite content with it. I can re-encode a DVD, have Azureus running, download from the Newsgroups, AND surf or do whatever all at the same time and nothing seems to slow it down and I don't ever run into problems. It multi-tasks like nobodies bidness. :thumbsup:

I had a non-HT Northwood 2.4 P4 before this and it would have issues when I tried to do too many things at once. I have another machine with an AMD Barton 2500+ and it is very similar to my old non-HT NW P4 performance-wise which one would expect.

The new high-end FX AMD cpu's are just a little outside of my comfort zone as far as price goes although I am sure they would give my HT P4 some serious competition.

 

[IntelUser2000]

The real name for Hyperthreading is Simultaneous Multi-Threading. Basically, its useful in processors that have lot of idle execution units. That not only applies to CPUs with extraordinarily long pipeline stages like Pentium 4, especially Prescott. It applies to very wide processors(wide meaning lot of execution units), like Power 5 and Itanium.

Extra 11 stages in Prescott isn't the only slow down.
(By the way I have looked at Hot Chips presentation, and one of the new features in Prescott that isn't mentioned in Prescott over Northwood is the 2x clocked AGU.)

Northwood to Prescott:
2x AGU(From 1x the clock)
Double the L1 Data cache with more than twice the latency
Double the L2 Cache with 1.8x latency
31 stages rather than 20 stages like Northwood
Better branch prediction(I think around 20%)

Those are the most important ones. Looking at Prescott benchmarks, the increase in cache latency ALONE makes Prescott slower. If the cache latency remained same, its very likely Prescott will be faster per clock compared to Northwood.

 

[clarkey01]

Does cache and cache latency affect clcok speed in anyway ?

Is it harder to scale with more cache ?

 

[blinky2004]

From the results I've seen, in some cases HT helps, some it makes no difference and some it actually hurts. This actually makes sense.

From my (limited) understanding it uses some of the pipelines which aren't normally used (most apps aren't that CPU intense) for the symmetric branching and to make the virtual CPU. It therefore follows that if the application would use all the pipelines efficiently in non-HT mode then enabling HT would harm the performance.

From a comment earlier, Adobe apps almost always run better on Intel processors. I have seen it written that Intel actually write a lot of the code for the PC versions of Adobe Software, but I not sure how true that is.

Countless benchmarks also show P4's have the edge over AMD for video apps.

To make full advantage of SMP / SMT not only does the operating system but also the application(s) need to be able to use both processors (i.e. SMP aware). Otherwise, one CPU does most of the work and the other sits largely idle. I have seen systems where this occurs.

 

[Wedge1]

Originally posted by: Wedge1
Guys I have a question about enabling/disabling hyperthreading. I have read elsewhere (erroneously perhaps, not sure) that enabling hyperthreading in the BIOS will not work unless you install the operating system AFTER enabling it. Same would go for disabling, i.e., changing it means re-installing the OS for the change to take effect. Or, said conversely, have it at the appropriate setting before installing the operating system in order for it to work.

Is this true or is it rubbish?

Bump for an answer to this question.

 

[Conky]

Originally posted by: Wedge1

Originally posted by: Wedge1
Guys I have a question about enabling/disabling hyperthreading. I have read elsewhere (erroneously perhaps, not sure) that enabling hyperthreading in the BIOS will not work unless you install the operating system AFTER enabling it. Same would go for disabling, i.e., changing it means re-installing the OS for the change to take effect. Or, said conversely, have it at the appropriate setting before installing the operating system in order for it to work.

Is this true or is it rubbish?

Bump for an answer to this question.

This is not true.

I am still living with a previous XP Pro install and the major change was my new HT P4 from a non-HT P4. Windows detected the HT P4 and reported 2 cpu's as did the bios. As Windows is famous for, it detected everything and adjusted accordingly. 🙂

It can be disabled in Windows options but honestly I have never tried to disable it. I have no reason to doubt it wouldn't be disabled if the O/S gives this option. My mobo bios(Asus P4P800) also has an option to disable HT but again, I have not explored this option.

I was pleased to know that I didn't have to reinstall Windows XP to get HT. :thumbsup:

 

[Rock Hydra]

Wedge1:
If HT it enabled when Windows is installed, it installs and runs a service that takes advantage of HT. You can disable HT in BIOS, but the HT service that runs unecessarily eats up extra RAM.

I got no Multitasking benefit from using HT, so I turned it off and I notice my computer is a little more responsive. It all depends on of there actually are idle clocks, if there aren't, even with HT enabled, there is no benefit.

 

[Wedge1]

Thanks guys. I checked it out from Windows and it is showing 2 CPUS, and so is CPU-Z.

But in case some of you have trouble enabling it for some reason, you might to use this guide if you are experiencing difficulties.

 

[Sc4freak]

Originally posted by: Wedge1

Originally posted by: Wedge1
Guys I have a question about enabling/disabling hyperthreading. I have read elsewhere (erroneously perhaps, not sure) that enabling hyperthreading in the BIOS will not work unless you install the operating system AFTER enabling it. Same would go for disabling, i.e., changing it means re-installing the OS for the change to take effect. Or, said conversely, have it at the appropriate setting before installing the operating system in order for it to work.

Is this true or is it rubbish?

Bump for an answer to this question.

Rubbish. Tried it myself, just go into BIOS, disable, and restart normally.

 

[IntelUser2000]

clarkey01: "Does cache and cache latency affect clcok speed in anyway ?

Is it harder to scale with more cache ?"

Apparently it is related. When cache is slow and other parts of the CPU is faster than the cache, then the cache would hamper the CPU from reaching higher clock speeds. And in case of Prescott, lower speed caches(whether latency or clock speed) would have lower power dissipation, which seems the only reason why Prescott can't increase in clock speed so much.