P4 and Hyperthreading
 

Folks:

This may be obvious, but do all P4's have hyperthreading?

--Tso

I think so...

no, not _all_ P4s have it. . .

Well yes and no. Yes they all have the wiring for hyperthreading but Intel picked certain models to activate the wiring at the factory. No you can not take a 2.0A GHz processor and activate hyperthreading. Also the motherboard have to support hyperthreading for the processor to take advantage of it. IMO, hyperthreading is a gimmick just to sell the processor and it is slower than using two physical processors.

Is there some command, script, etc. a la cpuinfo that can tell you if hyperthreading is enabled? I'm just deciding what services I should have running...

Thanks for the input, folks!

On my dell 8300 p4 3.00 in bios under cpu hyperthreading is enabled or not.

Check the BIOS on your system...if your CPU is hyperthread capable then you should be able to turn it on and off....if you don't have that option then your CPU probably isn't hyperthreaded. All systems that have Hyperthreaded CPU's need to have the ability to turn hyperthreading on and off in their BIOSes. Not all operating systems and softwares play nice with Hyperthreading.

If you have a CPU that is hyperthreaded you'll notice two things in Linux:

1) The operating system will see double the amont of installed CPU's and most likely install an smp kernel by default.

2) If you are booted to this smp kernel, then you will see two CPU's when running the following command:

cat /proc/cpuinfo

....and the earlier posters are correct....not all P4's are hyperthreaded. If you P4 system was built before late 2002, then it probably isn't HT capable.

Thanks for all the info. Appreciate it.

One thing to note...

Someone said that "all" P4s have the "wiring" for HTing. This is not entirely true. . . The first core used for the P4 (wallamite, but to hell with spelling) found in socket 423 and early 478 P4 systems did not have the "wiring" for HTing. It was the Northwood core that had the "wiring" and then in the core's mid life it was enabled on some chips. And by 'some' I mean, the more costly ones... hehe.

....and although a HT cpu may not be as fast as two physical cpu's, it is still a substantial speed improvement and I'm very impressed with a P4 3Gig HT cpu on a Linux box.........:D

Dutch

Although I'm not a hardware junky, it seems like a good idea to me. Although people might make the case for it being a sales gimmick, it can be said that every new innovation is a gimmick to sell computers.

a friend of mine that works for intel benchmarks stuff like that, and sent me some of the results. some apps that support threading well can get up to close to a 2x speed improvement. i forgot what kind of stuff is helped the most, but some things are. a few things are slower.

All I know is what took 10+ seconds on my previous P4 (such as parsing syslogs or refreshing rpm database package lists) now takes about 4 secs. Also KDE starts up in less than half the time.

If that's a gimmick, I'll have another! :D

D

Q: "Do all P4's have hyperthreading?"
A: No.

This Intel product spec sheet as well as this secondary article indicate which do and which don't. I've got an older P4 (2.4 B, purchased in Jan 2003) and it lacks HT. Oh well, hope this is of interest. -- J.W.