
Skylake CPUs have 'inverse Hyper Threading' to boost single-thread performance - kbd
http://www.myce.com/news/skylake-cpus-have-inverse-hyper-threading-to-boost-single-thread-performance-77011/
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nkurz
An interesting idea to ponder, but this isn't a feature present in Skylake or
any other processor Intel has announced. The German language source cited in
this link retracted their guess a few days later:
[http://www.heise.de/newsticker/meldung/IDF-2015-Intel-
enthue...](http://www.heise.de/newsticker/meldung/IDF-2015-Intel-enthuellt-
ein-wenig-die-Skylake-Architektur-2784862.html)

"Inverses Hyper-Threading, wie hier aufgrund von merkwürdigen Messergebnissen
spekuliert wurde, unterstützt der Skylake indes nicht."

"Inverse Hyper-Threading, as was speculated here due to strange measurement
results, is not supported by Skylake."

Here's some English language reporting about the retraction:

"However, Intel has dismissed rumors of Inverse Hyper Threading being present
on the Skylake die, something that we talked previously as being a cutting
edge methodology of single-thread computing boosting via multi-core help. We
expected an answer on this matter at IDF and Intel unfortunately dismisses it
as being false. Recent studies made by Heise.de showed incredible single-
thread computing performance by the new Core i7-6700K and speculated that
Inverse Hyper Threading might be present on the new Skylakes. Apparently, it
was not."

[http://news.softpedia.com/news/intel-reveals-the-skylake-
inn...](http://news.softpedia.com/news/intel-reveals-the-skylake-
innards-489560.shtml)

~~~
cm3
Yes I remember the heise reports as well and it was super speculative back
then. BTW, your English translation is good. May I ask if that is just with
high school German class or have you been to Germany?

~~~
nkurz
I'm American and took a year of German in college, but I cheated here. I
scanned the page to find the right sentence, and then copy-and-pasted it into
Google Translate. Then I fixed up the English to sound better while trying to
stay faithful to the phrasing in German. Without Google's starting point, I'd
have been guessing a lot, and probably wouldn't have shared a translation.

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dosshell
I strongly believe that if this feature exists Intel would be making a big
deal of it to get people to upgrade - not hide it. Therefor this is nonsense.

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jupp0r
The article is entirely speculative. Another entire speculative explanation
would be that Skylake simply has better power management allowing single cores
to operate at much higher frequencies when other cores are disabled.

Occam's razor (and my background in hardware design and high performance
computing) would definitely make me bet my money on the above speculation :)

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timthorn
Or it might just be that when multiple cores are in use, thermal
considerations require throttling back from full performance?

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cm2187
That wouldn't explain the jump in performance between generations of
processors.

~~~
wtallis
The change from 22nm to 14nm would.

~~~
cm2187
Smaller lithography means less heat dissipation, but the frequency hasn't gone
up, the processors executes the same number of instructions per second,
doesn't it?

~~~
creshal
Recent Intel CPUs with Turbo Boost have a frequency range they can operate on,
with a spread of over one GHz for some models. Thermal limits dictate how much
of this buffer the CPU is able to use, so better thermals do lead to higher
frequencies used.

~~~
cm2187
I am a bit outside of my area of confidence but isn't the turbo frequency the
max frequency advertised by intel on the CPU? There is not a ratio of 2.5
between these two models so it can only explain a fraction of the delta.

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wtallis
Seven months old. If there were any truth to these claims, more convincing
evidence would have surfaced by now.

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robinhoodexe
Had my hopes up for a short while... You'll loose in Dwarf Fortress sooner or
later due to "FPS-death" and DF is single-core only.

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foota
Is it possible there are shared units between cores? Not a hardware expert but
like shared arithmetic units or the like.

~~~
wtallis
Shared units between cores can be done and has been done, by AMD. It's hard;
AMD didn't do a great job of it. Intel didn't even try.

~~~
creshal
And AMD has given up on it, their next-gen Zen CPU will use a more
hyperthreading-alike architecture.

Only caches and memory/IO controllers are usually shared between cores.

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NamTaf
My guess is an architecture change that allows more of the 'shared' resources
to be used by a single core rather than rigidly enforcing a subdivision of the
resources between each core.

Sort of like if you had 2MB of cache per core vs a shared 8MB cache between 4
cores.

