Again, only real-world tests will show how valid the claims made by Intel and Microsoft are - and whether they make a difference when so much system power is drawn by, say, the display, a device that's consuming Watts whether the CPU's on a light load or a heavy one.
Snow Leopard's Grand Central Dispatch system, which allows software developers to stop worrying about threads at all and leave it all to the OS has the potential to allow Mac OS X greater control over thread scheduling, but it's not clear from Apple's GCD documentation whether its scheduler is as HT savvy as Windows 7's is.
Only four threads to schedule? Thread Parking ensures they'll only be assigned to physical cores
The Nehalem-derived Xeon 5500 processors Apple builds into the Mac Pro and Xserve have HyperThreading, though the CPUs in none of its other machines yet do, so this feature shouldn't be alien to Apple.
Linux certainly does support HyperThreading and has for years. It has also supported thread parking for quite a while too, kernel scheduler hacker Ingo Molnar told Register Hardware.
Indeed, the next major kernel release, 2.6.32, due in December, will include "further tweaks" for SMT load-balancing, he said, allowing the scheduler to "adapt to the momentary performance profile of each socket, core (and thread) on the system - even if they are asymmetric".
In short, it'll not simply favour real cores over virtual ones but also faster-running physical cores over slower ones, monitoring the state of each and switching threads as each core's frequency changes. The feature will be built into 2.6.32 but disabled by default. ®
Idle wild: how Intel's mobile Core i7 speeds up to slow down
COMMENTS
Its all in the leakage...
Modern <=90nm silicon processes no longer lose most of their energy in switching gates (more is the pity) but in simple leakage across the transistors. This exponentially increases as things are made smaller and exponentially increases with temperature. The energy loss happens even if the gates are "idle"!
Fast logic transistors == horrible leakage
So to solve this problem engineers add header and footer power switch transistors (bad logic transistors, so slow) to turn "hard off" whole sections of circuit. This Intel strategy means Intel can have its cake and eat it too.
Running some cores faster and turning "hard off" others saves all that lovely "idle" leakage. The thermal mass of the packaging and die will prevent excessive temperature rises in that one core saving exponential thermal effects.
Awesome,
M
RE: Physical cores vs. Virtual (hyperthread) cores #
If Windows sucks because it is just now releasing an OS that differentiates between physical and virtual cores, where does that leave Mac? The article handed you a pro-Linux talking point on a silver platter. Did you miss the preceding paragraph about Apple’s grand central dispatch? If your thinking was less Microsoft-centric your OS of choice might be taken more seriously.
Hmm
Sounds more like they underclock under normal circumstances and return to normal speed when needed.
The turbo boost sounds more like a marketing gimmick to me - 'slows down to cool down' won't sell as many chips!
@soft electrons
It very much depends on use case & how well the power is managed. If you double the clock & run for half the time then yes energy used is same or greater (depending on voltage) but, with good power managment, if you run fast there is more opportunity to sleep longer & deeper.
