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IDF August 2005 :: Next Gen - No Hyperthreading (HT) for Intel

by David Ross on 23 August 2005, 00:00

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Intel ditch HT technology

IDF Logo Intel have just stated that HT is not going to feature in their next architecture. This is a bit of a shock since they spent months messaging us that HT would be the most important move in microprocessor development, Intel have removed it (read - not included it) in their next generation processor.

Whilst this does not mean it won't ever be included, it is clear that there are currently no plans to include it. The reasoning for this is that it was a bridging technology to bring multi and dual core to us all.

HEXUS remembers that at the time Intel were very keen to inform us that there was no cost associated with HT and it was 'free' performance. Surely it should be on all platforms still?

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HEXUS Forums :: 12 Comments

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I'm something of a simpleton on this subject, and I have little doubt the more expert of you will correct me if I'm wrong on this, but I think Intel's abandoning of HT is due to efficiency of transistor count when considering future designs using 4 or more real cores. I'm not sure of the transistor count impact that HT has on current CPU's, but I suspect that perhaps the cost of 4 cores with HT on all 4 cores may take the die space of what could have been a 6 real core CPU (this all theoretical on my part as I have no clue, once again, of the cost per core to implement HT in transistors).

I have to say that was all TOTAL suposition on my part as I'm missing alot of important pieces of the puzzle on this, but I do think efficiency in multi core somehow has to figure into this descision to drop HT by Intel. There's no question a dual core CPU without any form of HT smacks a single core, HT enabled CPU all over the place in every benchmark I've seen published on the net except in the RAREST of cases. If this trend carries forward into multicore versus multicore with HT, new designs may benifit from not wasting space on HT functions that could be used for more cores instead when factored out over 4 or more cores. The only reason a P4 D EE has dual core AND HT is that Intel already has the HT transistors in place and might as well use them, and disable them on the regular Pentium D to differentiate the products only.

In a dual core design that is intended to end there, this is just good business since thier not planning on sticking to netburst as thier core design anyway. But with a new core, or even a redesigned one for multicore use, triming up the individual cores of all detrius like HT units and who knows what else they could get away with streamlining out, would be one of thier concerns I would think.

Just my 2 cents, that may be all it's worth ;)

Edit: If it's really as bada$$ as I expect it to be (here's hoping), I may FINALLY decide to buy a Intel product. I respected them alot in the P3 versus K7 days, here's hoping to see another one of those old time neck and neck battles that had us all on the edges of our seats. There's no question that the P6 cores have always rocked and it's newest revival in multicore, 64 bit, and on the P4's FSB will be a sweet setup and will be good for Intel.

Some more info from IDF 05 - Intel looks to be seriously concentrating on power issues this time around. The new chips allow cache to shared between cores when needed, and also allow for cache voltage to be lowered. Unused cores can also be powered off by the OS.

Sounds like Intel chips are getting cooler - quite literally.
I think they are doing this for marketing reasons.

My understanding is that the extra transitor count needed to add HT to a core is minimal, so once they have got HT debuged and working, there is no good technical reason to leave it out.

However, on most desktop benchmarks it makes little difference, and often degrades performace, so there is little point in having it in a $499 dell for J.Random Luser.

Instead, Intel will be keeping HT as a preemium feture for use in servers, and high end desktops, where it can make a significant difference, for use by costomers who know to configure their systems correctly.
The new chips allow cache to shared between cores when needed

wasn't hyperthreading disabled on recent BSD-based oses due to this horrendous potential security hole?
wasn't hyperthreading disabled on recent BSD-based oses due to this horrendous potential security hole?
No, someone pointed out on the Linux kernel mailing list, that there is a small, but theoreticaly possible security issue if a trusted and untrusted process are running concurently on a hyperthreaded CPU.

It was shown, that the untrusted process would be able to get clues about what the trusted process was doing, by comparing the cache latency of different memory accesses, as clearly if the trusted process had allready put some data in the CPU's cache, then the untrusted process would get it much faster. This could be used to leak confidental data in a shared hosting environment for example.

Clearly the same issue would apply to dual core CPUs where both cores share the same L2 Cache, such as current Athlon X2 designs.

Having said all that, this is all theoretical, and as far as I am aware, no one has produced any exploit code to demonstrate the issue.

There was talk a few months back about adding hooks to Linux, to allow security sensitive processes such as password or login, to request that no untrusted processes be scheduled on the same CPU while they run, but as far as I am aware, this has not been implemented.