Hyperthreading - is it a big deal?

[Jeff7181]

Originally posted by: Duvie
As Jeff says and I will agree the P4's HT is just a way to make the architecture mpre eefificent to overcome the huge latency penalties it takes from an enlarged pipeline and branch mispredictions. That aside it comes through and has a side benefit that it can help when 2 or more heavily cpu intensive apps work.

The Prescott's L2 cache also has higher latency than the Northwood's. This, combined with the 50% longer pipeline would have made it A LOT slower than a Northwood if there was no improvements made to HT and the branch predictor.

 

[Duvie]

Originally posted by: Jeff7181

Originally posted by: Duvie
As Jeff says and I will agree the P4's HT is just a way to make the architecture mpre eefificent to overcome the huge latency penalties it takes from an enlarged pipeline and branch mispredictions. That aside it comes through and has a side benefit that it can help when 2 or more heavily cpu intensive apps work.

The Prescott's L2 cache also has higher latency than the Northwood's. This, combined with the 50% longer pipeline would have made it A LOT slower than a Northwood if there was no improvements made to HT and the branch predictor.

Good point...whilei tis slower and more so at lower speed (2.8's), the gap starts to close on the higher endof 3.6ghz....Still I have seen an equally northwood seem to beat prescotts still at this level...

IMO, as an obvious non AMD fanboy to most around here...prescott was failure, among a heavy string of them late...hence I am using an AMD right now...

Waiting for the apologies from many who called me a fanboy in the past with my p4 threads. Obviously not. I showed no brnad loyalty like most here and went with what I felt was the better product and choice for the near term...

 

[Jeff7181]

Yes, I don't remember which site it was, maybe THG... but one of them estimated that the Prescott would need to reach 4 GHz for the cache latency to be equal to that of a 3.2 Northwood.

 

[cmv]

It depends on what operating system you use. There are marginal benefits with Windows but it has been found that there is 0% benefit with Linux because it can already switch processes so quickly that Hyperthreading has no advantage (actually, I think a slight disadvantage with the additional overhead).

 

[Jeff7181]

Originally posted by: cmv
It depends on what operating system you use. There are marginal benefits with Windows but it has been found that there is 0% benefit with Linux because it can already switch processes so quickly that Hyperthreading has no advantage (actually, I think a slight disadvantage with the additional overhead).

Hyper-Threading in the Pentium 4's case doesn't have much to do with the OS. It's a method of masking high latency.

 

[Duvie]

Originally posted by: Jeff7181

Originally posted by: cmv
It depends on what operating system you use. There are marginal benefits with Windows but it has been found that there is 0% benefit with Linux because it can already switch processes so quickly that Hyperthreading has no advantage (actually, I think a slight disadvantage with the additional overhead).

Hyper-Threading in the Pentium 4's case doesn't have much to do with the OS. It's a method of masking high latency.

well at least some OSes will not recognize it....Need Win xp home or greater, with support for it in win2k, but all reports I have ever seen was it had some issues....

I think the OS has something to do with it, but I am not sure of the technical reason.

 

[Jeff7181]

Originally posted by: Duvie

Originally posted by: Jeff7181

Originally posted by: cmv
It depends on what operating system you use. There are marginal benefits with Windows but it has been found that there is 0% benefit with Linux because it can already switch processes so quickly that Hyperthreading has no advantage (actually, I think a slight disadvantage with the additional overhead).

Hyper-Threading in the Pentium 4's case doesn't have much to do with the OS. It's a method of masking high latency.

well at least some OSes will not recognize it....Need Win xp home or greater, with support for it in win2k, but all reports I have ever seen was it had some issues....

I think the OS has something to do with it, but I am not sure of the technical reason.

The OS has to support multi-threading, but beyond that from what I understand, Hyper-Threading creates sort of a queue so that when the pipeline stalls while processing one thread, it can immediately switch to the other thread so you don't get too many "bubbles" in the pipeline.

 

[Duvie]

So the thread scheduler we must be talking about is clearly a hardware thing, right???

 

[Jeff7181]

Originally posted by: Duvie
So the thread scheduler we most be tlaking about is clearly a hardware thing, right???

Yes... at least that's the way I understand it.

*EDIT* And actually I misspoke in my previous post. Hyper-Threading doesn't just switch between threads when one stalls... it's actually capable of executing instructions from two separate threads at the same time.

 

[orion7144]

Originally posted by: Jeff7181
Yes, I don't remember which site it was, maybe THG... but one of them estimated that the Prescott would need to reach 4 GHz for the cache latency to be equal to that of a 3.2 Northwood.

This is why I decided to go back to my setup. With my 2.8E at 3.7, the higher FSB makes up for the latency issues. So my "3.7" is alot faster than say a 3.6 at default FSB. Yes, I am on water and able to keep the temps down. Of the 2 A64's I had, one of them did not OC well and the other was a DTR in a laptop that was dog slow.

 

[Duvie]

Ocing to 2.6+ghz has obvioulsy help since it puts it on par with more of a 4-4.2ghz p4. The reason why my 3.5ghz with HT usually loses in benches to this but in few occasions where I got the 22% increases with HT enabled the 3.5ghz actually is right there with this system...

Multitasking is a different beast though....

 

[Accord99]

Originally posted by: cmv
It depends on what operating system you use. There are marginal benefits with Windows but it has been found that there is 0% benefit with Linux because it can already switch processes so quickly that Hyperthreading has no advantage (actually, I think a slight disadvantage with the additional overhead).

This is completely wrong, and Linux's scheduler is nothing special, having only recently gotten comparable in performance to the scheduler that Windows has. HT benefits with two simultaneous CPU intensive on threads or processes recent Linux builds are comparable to that of Windows.

http://www.2cpu.com/articles/41_1.html

 

[carlosd]

Believe me the benefit is pretty marginal. HT is useless.

 

[clarkey01]

Originally posted by: carlosd
Believe me the benefit is pretty marginal. HT is useless.

Think your wrong on that one. Infact I am not flaming you, but it seems a fairly fan boyish thing to say, and hell I have been known to show some. But even a die hard AMD fan like myself who actaully has a 2.8 C and a 2000+, take it from ME I choose to burn my cd's, run norton, and rip cd's at the same time on 2.8C for a very good reason.

My 2000+ (yes Its not a fair putting a 2000+ Vs 2.8 Ghz P4C) stops when I run norton and try and open a folder. Really, its as if God replaces the CPU with a 266 Mhz Celeron (the one with no cache) in my rig instead. It sloooooooooows down my freind. In my 2.8C, it hardly lags.

 

[carlosd]

Ok. I am actually talking about athlon 64 CPUS not athlon XP. Besides you cannot compare a 2000+ CPU with a 2.8GHz. Just compare it with something like an athlon 64 2800+, and you would not see defference at all between these two CPUs running those light tasks(which are no CPU dependant at all). In fact you'll see the athlon 64 being more responsive.

 

[Zebo]

Originally posted by: Vee
How long have you used computers?
HT only exist on Pentium 4, and only on the P4C with 800FSB, 3.06GHz with 533FSB, P4E and P4F. So if you have any other Intel CPU or have ever had any other Intel CPU, you already know what a CPU lacking ht feels like. You also need WindowsXP with HT enabled, so again, if you've ever had any other OS, you already know what no ht feels like.

CPU lightweight things like surfing and editing some text, is IMO not really disturbed by background tasks, even if you lack ht.

There are benchmarks featuring multitasking. Veritest Winstone2004 and SysMark2004. Problem is their scores don't tell the subjective feel of this, and A64 does pretty good on them.

In some very special situations, it can be a big deal. But normally, I don't think it's any deal at all.

Exactly I agree with Vee. And A64's incredibly low latency (about 3x faster than compitition) you will "feel" all the time, any OS, any app making A64 much more snappy... Usually even in most multitasking situation.

 

[Lord Banshee]

I have to say HT is something very USEFULL.

I have a A64 2800+ at home and a p4 2.8 Northwood. Multi-tasking is alot easier on the p4 system with HT enabled. I can feel the difference.

Even with both machines overclocked the p4 likes to multi-task better then the A64. This is my personal experience. But do my A64 doesn't stand still when tring to do more than one thing at a time like the pervious stated 2000+. There is just a little lag. The lag is less and less with the increase in core speed. Is it worth crying about NO. Would it be nice for AMD to have something like this when the A64 came out yes. But in less than a year from now there will be Dual-Core A64 desktop CPUs and nothing is better than two real CPU cores.

 

[uOpt]

Hypterthreading has few to do with support for thread in the OS.

What Hyperthreading requires is an OS with a SMP (multiprocessor) capable kernel.

Even though none exists an OS with SMP kernel but no threading for userland would still benefit from hyperthreading when you run multiple CPUintensie applications. In fact, while all modern OSes have threading support most applications don't use it.

Now, inside the kernel you can have a kernel architecture based on threads, or on event loops or a mix thereof but that only make SMP more or less effective if the userland processes you want to run do a lot of system calls. This detail is hidden from the user and again, a hyperthreaded CPU looks like a SMP system even if your kernel internally is not threaded.

 

[clarkey01]

Originally posted by: carlosd
Ok. I am actually talking about athlon 64 CPUS not athlon XP. Besides you cannot compare a 2000+ CPU with a 2.8GHz. Just compare it with something like an athlon 64 2800+, and you would not see defference at all between these two CPUs running those light tasks(which are no CPU dependant at all). In fact you'll see the athlon 64 being more responsive.

My 2.8 C will still multitask better then an athlon 64, and thats even a hard pill for me to swallow.

I'd write more but im off to the pub to watch the united(soccer game to you folk), laterz

 

[ribbon13]

Once you have a dual opteron, these discussions are just entertainment.

 

[bigal40]

Originally posted by: Wisey
I have a HT enabled CPU with WinXP, so I know how it feels. I just don't know how it feels like on a AMD64 without it...

You can disable HT and then re-enable and see if you notice a difference

 

[Camofrog]

I use a p4 2.4c (o/c'd to 3.0) at home and a Athlon 2800+ at work. ( both have 1gb of PC3200 RAM)

I do a fair amount of multitasking on both and can duplicate the exact same things.

so a typical computer session for me;

Running: Autocad, Windows media player(music or video), surfin da net( several IE pages open usually), Microsoft Outlook, Excel, MSN, Xfire, Norton, Paintshop pro 8, My Documents(explorer), ventrilo, & finally Nero- burning a CD......( prob some other background programs usually)

Now i dont think that is that un-realistic?

and i will say that my AMD cant even come close to doing that while my P4 can, the AMD slooooows way down and u start getting blank windows and stuff, especially if u try to switch between stuff, it doesnt totally crash but it can be frustrating.

All tho i am also a gamer and would consider a AMD 64 machine simply for that, but i would keep my P4 around for anything else i need to do.

so theres my comparason.

 

[VirtualLarry]

Originally posted by: Camofrog
and i will say that my AMD cant even come close to doing that while my P4 can, the AMD slooooows way down and u start getting blank windows and stuff, especially if u try to switch between stuff, it doesnt totally crash but it can be frustrating.

"Blank windows"? You have other problems going on there with your system, it has nothing at all to do with HT support or not. Sounds like you might be running out of GDI resources to me.

 

[Jeff7181]

Originally posted by: Camofrog
I use a p4 2.4c (o/c'd to 3.0) at home and a Athlon 2800+ at work. ( both have 1gb of PC3200 RAM)

I do a fair amount of multitasking on both and can duplicate the exact same things.

so a typical computer session for me;

Running: Autocad, Windows media player(music or video), surfin da net( several IE pages open usually), Microsoft Outlook, Excel, MSN, Xfire, Norton, Paintshop pro 8, My Documents(explorer), ventrilo, & finally Nero- burning a CD......( prob some other background programs usually)

Now i dont think that is that un-realistic?

and i will say that my AMD cant even come close to doing that while my P4 can, the AMD slooooows way down and u start getting blank windows and stuff, especially if u try to switch between stuff, it doesnt totally crash but it can be frustrating.

All tho i am also a gamer and would consider a AMD 64 machine simply for that, but i would keep my P4 around for anything else i need to do.

so theres my comparason.

So you watch movies or listen to music while you run auto CAD with Outlook open in the background while you're working with an Excel spreadsheet while you're running a virus scan while you edit photos in PSP8 while you browse your My Documents folder while you listen in on a ventrillo server while you burn a CD while you browse the internet while you chat on MSN??????

I don't mean to be rude, but that sounds like a load of BS.

 

[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...