What's the deal with hyper-threading?

[Vertigo1]

Hi,

Having recently switched from AMD to Intel, I'm wondering what the deal is with CCE and hyper-threading on the P4?

Compared to the AMD processor, the system stays lovely and responsive when encoding on the P4, but Task Manager only reports around 67% processor usage, rather than 100%.

Does CCE work well with HT or should I disable it for encoding runs? I quite like the extra responsiveness of the system with it enabled, so it's going to be a bit of a pain if I have to turn it off to do encoding runs all the time.

Ta for any info.

[br408408]

That's 67% of each processor, so while disabling HT may up your single CPU usage, it should slow down your encode speed. 66-67% in all I get on my HT P4, but even at that, my encode speeds are about 3.1 RT with CCE 2.5 and 3.5 RT with 2.67

[Vertigo1]

Thanks for that. Just did my own test with and without and it certainly is faster with HT enabled.

While you're here, can I ask one more quick question? Which is best to use, 2.5 or 2.67? It appears that a lot of people still use 2.5 or indeed both versions, when I'd have thought 2.67 would be better and everyone would just upgrade to that. What does 2.5 do that 2.67 doesn't to keep people using it?

Cheers.

[erdoke]

Originally posted by Vertigo1

While you're here, can I ask one more quick question? Which is best to use, 2.5 or 2.67? It appears that a lot of people still use 2.5 or indeed both versions, when I'd have thought 2.67 would be better and everyone would just upgrade to that. What does 2.5 do that 2.67 doesn't to keep people using it?


People who stick to 2.50 say it has better quality encodes. Others can't see no difference in quality, but they prefer the speed of 2.67.
Run some tests and if you are not able to find quality difference, use 2.67.

BTW 2.70 is out to make it more difficult.:)

[auenf]

essentially HT is only available on the P4's (notice its not available on the P-M ;)) cause the P4 was designed to reach 2ghz and 3ghz easily cause AMD beat intel to the 1ghz milestone. the P4's arch has a really long execution pipeline, and HT allows two individual 'threads' to be executed on the processor at once, which is only possible cause some executions are waiting for some previous ones to finish, and most of the time the P4 is only using 70% of its execution units. with HT it can easily use 90% of its execution units when a multithreaded app is running, (or multiple processes are running).

the P3, Athlons and P-M all have a 'normal' sized execution pipeline (ie, they are a lot faster than a P4 at equal MHz) so wont benefit from HT as much.

of course i could have dreamt it all...

Enf...

[KeyserSoze]

The Athlon XP has a ten stage pipeline while the Pentium 4 has twenty pipeline stages.( 30 on Prescot)
Largely because of its deeper pipeline, the P4 can reach higher clock speeds. However, missed predictions that cause pipeline “stalls” also cause a very significant twenty cycle delay in the Pentium 4 versus only a ten cycle delay in the Athlon XP.
So HT was created to compensate this problem and ofcourse Athlon don't need it at all!!!

[erdoke]

Originally posted by KeyserSoze

So HT was created to compensate this problem and ofcourse Athlon don't need it at all!!!

Yep. that's why dual Opteron is so powerful compared to a single CPU system and AMD is just about to enter the final designing phase of dual core Opterons. :D Not to mention dual Athlon-MP systems. Do you suggest they're senseless? (It is considerably the same multitasking gain)
I guess it's not so simple as you wrote.

[erdoke]

Sorry, it was a double post.

[KeyserSoze]

We are talking here about Hyper-treading and OFCOURCE SINGLE cpus!!!!

I really don't get the point of you respond;)


And ofcourse AMD don't need HT ...they already doing more calc/cycle than Intel....

[erdoke]

Multitasking is much more than HT. That's why it's not wise to say one or another CPU wouldn't need HT.
The definition of "single CPU" will change soon as well. Dual core CPU's knockin' on the door... ;)