The Return of Hyper Threading

While Nehalem is designed to scale to up to 8 cores per chip, each one of those cores has the hardware necessary to execute two threads simultaneously - yep, it's the return of Hyper Threading. Thus our quad-core Nehalem sample appeared as 8 logical cores under Windows Vista:


Four cores, eight threads, all in a desktop CPU

Note that as in previous implementations of Hyper Threading (or other SMT processors) this isn't a doubling of execution resources, it's simply allowing two instruction threads to make their way down the pipeline at the same time to make better use of idle execution units. Having 8 physical cores will obviously be faster, but 8 logical (4 physical) is a highly power efficient way of increasing performance.

We took Valve's source-engine map compilation benchmark and measured the compile time to execute one instance (4 threads) vs. two instances of the benchmark. The graph below shows the increase in compilation time when we double the workload:

Valve Map Compilation Benchmark - 4 to 8 Thread Scaling

While the 2.66GHz Core 2 Quad Q9450 (Penryn) takes another 127 seconds to execute twice the workload, the 2.66GHz Nehalem only needs another 49 seconds. And if you're curious, this quad-core Nehalem running at 2.66GHz is within 20% of the performance of an eight-core 3.2GHz Skulltrail system. Equalize clock speed and we'd bet that a quad-core Nehalem would be the same speed as an 8-core Skulltrail here. The raw performance numbers are below:

Valve Map Compilation Benchmark 

We couldn't disable Hyper Threading so we reached the limits of what we were able to investigate here.

The Socket A Quick Path to Memory
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  • Justin Case - Sunday, June 08, 2008 - link

    The chances of AMD dying are approximately... zero. The question is whether they stay as an independent company or get bought by someone else. Their IP and patent portfolio alone are worth more than the company's current value, even if they didn't sell a single CPU and didn't have any fabs.

    The top candidate is Samsung, followed by IBM, followed by the UAE. But the real nightmare scenario is this: Microsoft buys AMD, and slowly makes its software incompatible with (or run much slower on) everyone else's CPUs. After that, they have zero incentive to improve the chips, because no one else can compete anyway.

    Since it's been shown that Microsoft can violate antitrust legislation as much as it wants (as long as it pays off a few senators), this is not at all impossible. Be afraid. Be very afraid.
    Reply
  • VooDooAddict - Monday, June 09, 2008 - link

    That would be the beginning of the end for MS.

    MS buys AMD? .... that would be the day I buy a fully loaded Mac Pro.
    Reply
  • Griswold - Friday, June 06, 2008 - link

    Listenting to whom? Somebody as naive and clueless as you, who apparently believes breaking laws in the past should be forgiven and forgotten until there is no competition at all, because the market will magically make things work out perfectly for the customer anyway...?
    Reply
  • n0b0dykn0ws - Thursday, June 05, 2008 - link

    If Nehalem comes out and does run circles around current processors, then we're better off, right?

    The only problem is that Intel is holding back on it's CPUs.

    Without competition, Intel will only give us 'just a little taste'.

    Me personally? I want the full strength version at today's prices.

    n0b0dykn0ws
    Reply
  • Rev1 - Monday, June 09, 2008 - link

    AMd is still competitive in the price segment of lower end cpu's, and after the PT4 debacle intel doesnt wanna loosen it's grip anytime soon to AMD. Reply
  • Zurtex - Thursday, June 05, 2008 - link

    You've written:

    "Encoding performance here went through the roof with Nehalem: a clock for clock boost of 44%."

    But your graph shows the exact opposite. I'm assuming you just got the numbers on the graph the wrong way around, rather than your analysis mixed up.
    Reply
  • Ryan Smith - Thursday, June 05, 2008 - link

    Uh, sometimes bits get flipped when in transfer from Taiwan, yeah, that's it.

    Anyhow, thanks for the notice. Fixed.
    Reply
  • 8steve8 - Thursday, June 05, 2008 - link

    exactly what I expected.

    imc was long overdue for intel...


    can't wait to buy one, but I've been hearing us mere consumers wont be able to until well into 09?

    Reply

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