Dual Core 4 threads???

[jcbray]

Do you own a Pentium 4 with Hyper-threading? this will give the appearence of four 4 threads with two cores.

[jcbray]

Just to carry on from that quote, seen as it seems to be talking about hyper-threading - what it does is, simply put, to execute part of thread 1, then part of thread 2, at a fast enough rate that it give the appearence of running 2 threads, but still, only one is executed at once.

[dotTom]

Just to carry on from that quote, seen as it seems to be talking about hyper-threading - what it does is, simply put, to execute part of thread 1, then part of thread 2, at a fast enough rate that it give the appearence of running 2 threads, but still, only one is executed at once.

That's not quite true. Hyper Threading is an attempt to make better use of the functional units within a given cores instruction pipeline, if the code is correctly optimised for HT then it is possible to get true concurrency (for example executing a float and integer operation at the same time). I believe the old Netburst architecture has 2 integer ports and 1 floating port per instruction pipe, so if both threads on a single core HT Netburst try to do float ops at the same time then one will block. The ill fated Itantium (IA64) are more float ports per pipe, which is why HT makes more sense on that architecture.

Correctly optimised HT code can yield good wins - take a look the data Luxology presented at last years Siggraph demonstrating the scalabillity of their threading accross cores with and without HT enabled. Of course HT is a added extra and in no way matches the lovelyness of multi-cores.

[ExKArt]

So how come my Dual Core processor has 4 threads?

Non-technically

Single CPU single thread
edit: Single Cpu w/ HT 2 threads (one is virtual)
Dual Core two threads
Dual Core w/HT each four threads, I'm sure Intel's site or related will say something like that.

[Xecode]

Alrighty then, hurray for HT.

[kaiser_pro]

not quite, some programs/operations slow up due to HT

[Srek]

not quite, some programs/operations slow up due to HT

You got an example for this?

Cheers
Björn

[JDex]

You got an example for this?

Cheers
Björn

I've personally had some rendering results in Mental Ray that indicated this, the difference was nominal (< 2%) and it wasn't the case in every test. Different scenes produced varying results.

[Tlock]

HT can boost performance if code has be very properly designed for this, otherwise could cause occasional bottle necks. That is why some applications can gain exceptional results while others in the other extreme expierence slow downs.

HT splits commands to take advantage of unused resources to boost thread performance.

Dual Core is much better than just HT, but HT DC is a logical combination.

[andytw]

One example where Hyper-threading can decrease performance is when the two threads start to compete for the available cache. This can result in the CPU spending excessive time moving data in & out of cache rather than doing useful work.
More about Hyper-threading here (http://www.2cpu.com/articles/42_1.html) .

[lots]

One would say that dual core suffers from the starved bandwidth problem even more so than HT. At least in the case of Intel.

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