Is there HyperThreading in Intel macs?

From what I've read, the Yonah core is not HyperThread capable.

HyperThreading gives the Pentium processor the ability to emulate a second processor. Sort of useless with 2 real processors. 😟

Steve

I thought of that also. Unfortunately, HyperThreading never was the performance boost that it was hoped to be, and caused some problems with programs that expected only one processor.

Steve

Hyperthreading was designed as a way to get better scheduling behavior out of applications and operating systems that weren't very good at fully cooperative multitasking.

MacOS X is better at this than Win2K and Linux 2.2 were. It doesn't need this.

Sort of useless with 2 real processors. 😟

Not useless at all - HyperThreading doesn't emulate a second core as such, it just uses idle CPU cycles to execute a secondary set of instructions to make more efficient use of the CPU. This roughly equates to two logical processors on a single core, but it's no substitute for a dual-core/dual-cpu setup. There are Intel chips - the Pentium D and Xeon - that have HyperThreading
and dual cores, which produces a very efficient chip with few redundant CPU cycles. You can get Xeon servers that have two physical chips but eight logical CPUs - an 8-processor server for about £2,000 is pretty good 🙂 HyperThreading doesn't actually count as a proper second processor, it just looks like one, so the operating system doesn't need SMP support, as it's all handled inside the CPU.

Hyperthreading was designed as a way to get better
scheduling behavior out of applications and operating
systems that weren't very good at fully cooperative
multitasking.

No operating systems use cooperative multitasking since Windows 9x/MacOS 9, as it's a nastily inefficient and error-prone system. I can't comment on the comparative merits of Windows XP vs Mac OS X's handling of multitasking, but both were built to use preemptive multitasking.

HyperThreading doesn't really have much to do with either multi- tasking or operating system design, it's a form of simultaneous multi- threading, which simply means the ability to make better use of the CPU, to dedicate processing time to a second thread while the first is waiting for data.

The Pentium 4's implementation of HT is a little awkward and dependent on various software factors, but generally speaking simultaneous multi-threading is a good sort of thing to have.

Not useless at all - HyperThreading doesn't emulate a
second core as such, it just uses idle CPU cycles to
execute a secondary set of instructions to make more
efficient use of the CPU.

The Netburst architecture of the Pentium-D has a pipeline that is about 30 stages. The Core Duo is less than 1/2 of that. There is a lot more room for Hyperthreading in a 30+ stage pipeline than there is in a 14 stage. Intel concluded that Hyperthreading wouldn't be very effective on the Pentium-M based chips. Even on the Netburst architecture the number of situations where Hyperthreading improves performance is relatively limited. In no way does a Hyperthreaded architecture perform like a second core. At best it adds 10% to 15% improvement and in most cases much less. It can even slow down the some tasks in rare cases.

That's more or less making the same point that I was trying to make 🙂

(With a little help from http://en.wikipedia.org/wiki/Hyperthreading#Performance)

Nice article, though I love this part, "Intel claims up to a 30% speed improvement compared against an otherwise identical, non-SMT Pentium 4."

I'd suggest that no one has seen a 30% improvement in real life. The point about getting better performance if the OS knows about the HT thread vs. a real core is interesting though. I hadn't thought about that.

Hyper-Threading was never a 2nd core emulator at all. I'd be interested in seeing the article that said that. It's not true at all. In fact Ive never heard anyone ever say that it was such a thing.

Hyper-Threading technology improves processor performance under certain workloads by providing useful work for execution units that would otherwise be idle, for example during a cache miss.

Hyper-Threading was never a 2nd core emulator at all.
I'd be interested in seeing the article that said
that. It's not true at all. In fact Ive never heard
anyone ever say that it was such a thing.

Well it isn't that bad of a description. As far as the OS and applications are concerned, it looks like another processor.

Hyper-Threading was never a 2nd core emulator at all. I'd
be interested in seeing the article that said that. It's
not true at all. In fact Ive never heard anyone ever say
that it was such a thing.

Agreed - hey, Steve _hy, where'd this emulation theory stem from?

I'd suggest that no one has seen a 30% improvement in
real life. The point about getting better performance
if the OS knows about the HT thread vs. a real core
is interesting though. I hadn't thought about that.

Much as it shames me, I do have a modicum of Windows Server experience - of course, it could be any number of things, but HyperThreading on P4/Xeon chips did make a big difference in some server applications (Microsoft SQL Server and Exchange Server were particularly fond of it - I had to turn it off to troubleshoot some hardware problems once or twice) - with many user apps, though, you see one "processor" graph going crazy while the other stays at a flat 0%...

Hyper-Threading was never a 2nd core emulator at

all. I'd

be interested in seeing the article that said that.

It's

not true at all. In fact Ive never heard anyone

ever say

that it was such a thing.

In HyperThreaded desktops from Dell and HP when installing Oracle client we would run into licensing problems because it appeared to Oracle as 2 processors when HyperThreading was turned on in BIOS. Turning it off fixed all install problems. Additionally, MS made a licensing change for some of their software that required additional licences for HyperThreading which they do not require in actuality. You can Google much of this.
Also, Task Manager shows 2 processors on HyperThreaded machines that properly deal with this in BIOS.
None of this is anecdotal but based on supporting over 5000 workstations in approximately 500 locations.
HTH,

Steve

Agreed - hey, Steve _hy, where'd this
emulation theory stem from?

From the WikiPedia article referred to earlier in this thread:

This allows a Hyper-Threading equipped processor to pretend to be two "logical" processors to the host operating system

Except for its performance implications, this innovation is transparent to operating systems and programs. All that is required to take advantage of Hyper-Threading is symmetric multiprocessing (SMP) support in the operating system, as the logical processors appear as standard separate processors.

Steve