Some thoughts about Ivy Bridge

here in thread i'm going go little more detail misconceptions , things aren't understood intel's 2012 cpu code-named ivy bridge

namely, 1) benefits of new process technology, , 2) configurable tdp.

1. 22nm tri-gate process technology:

unfortunately, there's lot of misunderstandings benefits process technology generation gives. it's important understand gives cpu architects play around. whether potential realized story.

take @ curve graph 22nm:

it's important note voltage points. remember, there exist trade-offs. because 17w ivy bridge chips going macbook airs , ultrabooks noticeably faster predecessor, won't able scale down voltage, , save power.

thing says "37% faster"? well, that's @ low operating voltages. seems @ 0.7v. sandy bridge requires on 1v reach hfm(high frequency mode), highest base frequency, , same true turbo mode. gain closer 20%. operating frequency runs around 0.7v lfm(low frequency mode).

to wrap 2 points up:

a. gains nominal, nothing out of ordinary
b. won't see lower tdp, if @ all.

not mean "37% faster" won't taken advantage of. that's configurable tdp comes in. remember how said process technologies enable cpu architects "play around"?


2. configurable tdp

on ivy bridge mobile chips, there 3 tdp points, named ctdp down, nominal tdp, , ctdp up. 17w skus 3 tdp points 14w/17w/25w. each tdp points have own base clocks.

configurable tdp allows system designers "configure" chip around system want build rather doing other way, building chassis sku.

may ask what's difference throttling , turbo?

throttling: it's when chip reaches unsafe temperature, 90c
turbo mode: preset timers, power consumption, , upon reaching temperature that's not unsafe cpu, 60c

know turbo mode: know not guaranteed frequency. can ramp down. base clocks guaranteed frequency. both throttling , turbo mode plays around that.

important thing know turbo mode: it's response times. make system feel "snappier". oh, , system faster 95% of time since duration run system @ full versus duration don't run @ full less.

here's graph showing how ctdp works:

can see chip ctdp down loses turbo(compared nominal) on workloads allow chip reach max tdp, retain similar performance on workloads light enough below max tdp.

relation between ctdp , lfm: lfm frequency in nominal tdp base frequency ctdp down. 22nm transistor benefits mean higher frequencies possible @ ctdp down(compared if didn't have 22nm process).

configurability of ctdp can set manufacturer. trigger can be:
-environmental: meaning if switch tablet mode, notebook mode. notebook mode might have better cooling, can go ctdp down nominal, or nominal ctdp up
-manual: works turbo button user presses.
-fixed: manufacturer has set cpu @ tdp convenience of designing @ set frequency

configurable tdp summary: systems designed around worst case. allowing lower tdp figures using ctdp down, manufacturer can lower worst case , make thinner, sleeker system. ctdp allows faster operation when more cooling available, when docked better cooling. turbo clock speeds kept same benefit responsiveness, regardless of form factor/tdp.

if chassis allowing 14w had nominal 17w tdp chip in it, chip throttle, results in:

a: lower performance
b: higher chassis temperature

throttling on desktop processors happen @ around 80-85c. because cpu try reach maximum frequency against throttling mechanism, temperature stay @ temperatures until load reduced. in turn raise chassis temperatures beyond if wasn't throttling. lower performance due loss of turbo mode.

(of course, can put same chip in overspecced system, doesn't need it, absolute thin , light systems, lower tdp necessary. 1 can imagine "smaller 11" mba" mba in future )

 

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