CPU utilization


When we give a lot of load to CPU, the clock and VID goes up? Why it goes up with CPU usage?

Bertrand RussellAsked:
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slinkygnConnect With a Mentor PresidentCommented:
SpeedStep (really, Enhanced Intel SpeedStep Technology or "EIST" these days) allows the processor to dynamically reduce the clock speed of the chip from its rated value when utilization is low; TurboBoost allows for a brief, controlled increase in clock speed above its rated value when utilization is at its maximum.  So they're complementary technologies -- one for low and one for high utilization.

And VID/clock doesn't affect CPU utilization with these; it's the other way around.  The changes are near-instant, but the idea is,  when the CPU sees low utilization, it can underclock itself (which then permits it to undervoltage, for power savings), and it scales back up when it sees high utilization (again, increasing clock speed and if necessary voltage).
That is by design.  Intel chips use their SpeedStep and TurboBoost technologies to quickly, dynamically scale their clock speed on the hardware side (and, with that, voltage and thus thermal output) based on load for power savings.  AMD CPUs do the same with their Cool'n'Quiet and PowerNow technologies.
Bertrand RussellAuthor Commented:
Thanks for reply. I checked my code on Intel XEON machine. What is SpeedStep and TurboBoost? What is difference between them. Also, why VID and clock effect the CPU utilization?

Thank u
>>  Also, why VID and clock effect the CPU utilization?   <<  it is rather the other way round.
a cpu can run on low voltage when idle, but if you increase the load, the clock frequency is increased, so it can handle faster the load; this also increases the POWER the cpu needs.

speedstep technology :  http://en.wikipedia.org/wiki/SpeedStep
info from intel :  http://www.intel.com/support/processors/sb/CS-028855.htm
Bertrand RussellAuthor Commented:
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