Other Power Savings

Haswell's power savings come from three sources, all of which are equally important. We already went over the most unique: Intel's focus on reducing total platform power consumption by paying attention to everything else on the motherboard (third party controllers, voltage regulation, etc...). The other two sources of power savings are more traditional, but still very significant.

At the micro-architecture level Intel added more power gating and low power modes to Haswell. The additional power gating gives the power control unit (PCU) more fine grained control over shutting off parts of the core that aren't used. Intel published a relatively meaningless graph showing idle power for standard voltage mobile Haswell compared to the previous three generations of Core processors.

Haswell can also transition between power states approximately 25% faster than Ivy Bridge, which lets the PCU be a bit more aggressive in which power state it selects since the penalty of coming out of it is appreciably lower. It's important to put the timing of all of this in perspective. Putting the CPU cores to sleep and removing voltage/power from them even for a matter of milliseconds adds up to the sort of savings necessary to really enable the sort of always-on, always-connected behavior Haswell based systems are expected to deliver.

Intel has also done a lot of work at the process level to bring Haswell's power consumption down. As a tock, Haswell is the second micro-architecture to use Intel's new 22nm tri-gate transistors. The learnings from Ivy Bridge are thus all poured into Haswell. Intel wasn't too specific on what it did on the manufacturing side to help drive power down in Haswell other than to say that a non-insignificant amount of work came from the fabs.

The Fourth Haswell

At Computex Intel's Mooly Eden showed off this slide that positioned Haswell as a 15-20W part, while Atom based SoCs would scale up to 10W and perhaps beyond:

Just before this year's IDF Intel claimed that Haswell ULT would start at 10W, down from 17W in Sandy/Ivy Bridge. Finally, at IDF Intel showed a demo of Haswell running the Unigen Heaven benchmark at under 8W:

The chain of events tells us two things: 1) Intel likes to play its cards close to its chest, and 2) the sub-10W space won't be serviced by Atom exclusively.

Intel said Haswell can scale below 10W, but it didn't provide a lower bound. It's too much to assume Haswell would go into a phone, but once you get to the 8W point and look south you open yourself up to fitting into things the size of a third generation iPad. Move to 14nm, 10nm and beyond then it becomes more feasible that you could fit this class of architecture into something even more portable.

Intel is being very tight lipped about the fourth client Haswell (remember the first three were desktop, mobile and ultra-low-volt/Ultrabook) but it's clear that it has real aspirations to use it in a space traditionally reserved for ARM or Atom SoCs.

One of the first things I ever heard about Haswell was that it was Intel's solution to the ARM problem. I don't believe a 10W notebook is going to do anything to the ARM problem, but a sub-8W Haswell in an iPad 3 form factor could be very compelling. Haswell won't be fanless, but Broadwell (14nm) could be. And that could be a real solution to the ARM problem, at least outside of a phone.

As I said before, I don't see Haswell making it into a phone but that's not to say a future derivative on a lower power process wouldn't.

The New Sleep States: S0ix CPU Architecture Improvements: Background
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  • defiler99 - Tuesday, October 16, 2012 - link

    One of the best articles on Anandtech in some time. This is great original tech industry reporting. Reply
  • Gc - Saturday, January 12, 2013 - link

    Congratulations, an intel cpu engineer wrote around 27 Dec 2012:

    "... Anandtech's latest Haswell preview is also excellent; missing some key puzzle pieces to complete the picture and answer some open questions or correct some details but otherwise great. ..."

    http://www.reddit.com/r/IAmA/comments/15iaet/iama_...
    Reply
  • xaml - Thursday, May 23, 2013 - link

    This was first posted here a few handfuls of pages back as a comment by user "telephone". ^^ Reply
  • yhselp - Friday, March 29, 2013 - link

    A few questions.

    Is there going to be a replacement (37W) for the current IVB 35W quad-core part? Quite a few designs are now dependable on this, lower power quad-core option - Sony S-series and Razer Blade, to name a few.

    When can we expect all mobile CPUs (except maybe for the extreme series) to fall into the 10W-20W range? In three years' time and 10nm?

    The decision to not include GT3 with desktop parts is very disappointing. A 35/45W low-voltage part with GT3 would make for an excellent HTPC build, among other things. Is there a chance Intel change their mind and start shipping GT3 desktop parts at some point?
    Reply
  • JVimes - Tuesday, August 19, 2014 - link

    Does EU stand for Execution Unit? That was surprisingly hard to google for. Reply

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