Intel's Haswell Architecture Analyzed: Building a New PC and a New Intel
by Anand Lal Shimpi on October 5, 2012 2:45 AM ESTThe New Sleep States: S0ix
A bunch of PC makers got together and defined the various operating modes that ACPI PCs can be in. If everyone plays by the same rules there are no surprises, which is good for the entire ecosystem.
System level power states are denoted S0 - S5. Higher S-numbers indicate deeper levels of sleep. The table below helps define the states:
| ACPI Sleeping State Definitions | ||||
| Sleeping State | Description | |||
| S0 | Awake | |||
| S1 | Low wake latency sleeping state. No system context is lost, hardware maintains all context. | |||
| S2 | Similar to S1 but CPU and system cache context is lost | |||
| S3 | All system context is lost except system memory (CPU, cache, chipset context all lost). | |||
| S4 | Lowest power, longest wake latency supported by ACPI. Hardware platform has powered off all devices, platform context is maintained. | |||
| S5 | Similar so S4 except OS doesn't save any context, requires complete boot upon wake. | |||
S0 is an operational system, while S1/S2 are various levels of idle that are transparent to the end user. S3 is otherwise known as Suspend to RAM (STR), while S4 is commonly known as hibernate or Suspend to Disk (this one is less frequently abbreviated for some reason...).
These six sleeping states have served the PC well over the years. The addition of S3 gave us fast resume from sleep, something that's often exploited when you're on the go and need to quickly transition between using your notebook and carrying it around. The ultra mobile revolution however gave us a new requirement: the ability to transact data while in an otherwise deep sleep state.
Your smartphone and tablet both fetch emails, grab Twitter updates, receive messages and calls while in their sleep state. The prevalence of always-on wireless connectivity in these devices makes all of this easy, but the PC/smartphone/tablet convergence guarantees that if the PC doesn't adopt similar functionality it won't survive in the new world.
The solution is connected standby or active idle, a feature supported both by Haswell and Clovertrail as well as all of the currently shipping ARM based smartphones and tablets. Today, transitioning into S3 sleep is initiated by closing the lid on your notebook or telling the OS to go to sleep. In Haswell (and Clovertrail), Intel introduced a new S0ix active idle state (there are multiple active idle states, e.g. S0i1, S0i3). These states promise to deliver the same power consumption as S3 sleep, but with a quick enough wake up time to get back into full S0 should you need to do something with your device.
If these states sound familiar it's because Intel first told us about them with Moorestown:
In Moorestown it takes 1ms to get out of S0i1 and only 3ms to get out of S0i3. I would expect Haswell's wakeup latencies to be similar. From the standpoint of a traditional CPU design, even 1ms is an eternity, but if you think about it from the end user perspective a 1 - 3ms wakeup delay is hardly noticeable especially when access latency is dominated by so many other factors in the chain (e.g. the network).
What specifically happens in these active idle power states? In the past Intel focused on driving power down for all of the silicon it owned: the CPU, graphics core, chipset and even WiFi. In order to make active idle a reality, Intel's reach had to extend beyond the components it makes.
With Haswell U/ULT parts, Intel will actually go in and specify recommended components for the rest of the platform. I'm talking about everything from voltage regulators to random microcontrollers on the motherboard. Even more than actual component "suggestions", Intel will also list recommended firmwares for these components. Intel gave one example where an embedded controller on a motherboard was using 30 - 50mW of power. Through some simple firmware changes Intel was able to drop this particular controller's power consumption down to 5mW. It's not rocket science, but this is Intel's way of doing some of the work that its OEM partners should have been doing for the past decade. Apple has done some of this on its own (which is why OS X based notebooks still enjoy tangibly longer idle battery life than their Windows counterparts), but Intel will be offering this to many of its key OEM partners and in a significant way.
Intel's focus on everything else in the system extends beyond power consumption - it also needs to understand the latency tolerance of everything else in the system. The shift to active idle states is a new way of thinking. In the early days of client computing there was a real focus on allowing all off-CPU controllers to work autonomously. The result of years of evolution along those lines resulted in platforms where any and everything could transact data whenever it wanted to.
By knowing how latency tolerant all of the controllers and components in the system are, hardware and OS platform power management can begin to align traffic better. Rather than everyone transacting data whenever it's ready, all of the components in the system can begin to coalesce their transfers so that the system wakes up for a short period of time to do work then quickly return to sleep. The result is a system that's more frequently asleep with bursts of lots of activity rather than frequently kept awake by small transactions. The diagram below helps illustrate the potential power savings:
Windows 8 is pretty much a requirement to get the full benefits, although with the right drivers in place you'll see some improvement on Windows 7 as well. As most of these platform level power enhancements are targeted at 3rd generation Ultrabooks/tablets it's highly unlikely you'll see Windows 7 ship on any of them.
All of these platform level power optimizations really focus on components on the motherboard and shaving mWs here and there. There's still one major consumer of power budget that needs addressing as well: the display.
For years Intel has been talking about Panel Self Refresh (PSR) being the holy grail of improving notebook battery life. The concept is simple: even when what's on your display isn't changing (staring at text, looking at your desktop, etc...) the CPU and GPU still have to wake up to refresh the panel 60 times a second. The refresh process isn't incredibly power hungry but it's more wasteful than it needs to be given that no useful work is actually being done.
One solution is PSR. By including a little bit of DRAM on the panel itself, the display could store a copy of the frame buffer. In the event that nothing was changing on the screen, you could put the entire platform to sleep and refresh the panel by looping the same frame data stored in the panel's DRAM. The power savings would be tremendous as it'd allow your entire notebook/tablet/whatever to enter a virtual off state. You could get even more creative and start doing selective PSR where only parts of the display are updated and the rest remain in self-refresh mode (e.g. following a cursor, animating a live tile, etc...).
Display makers have been resistant to PSR because of the fact that they now have to increase their bill of materials cost by adding DRAM to the panel. The race to the bottom that we've seen in the LCD space made it unlikely that any of the panel vendors would be jumping at the opportunity to make their products more expensive. Intel believes that this time things will be different. Half of the Haswell ULT panel vendors will be enabled with Panel Self Refresh over eDP. That doesn't mean that we'll see PSR used in those machines, but it's hopefully a good indication.
Similar to what we've seen from Intel in the smartphone and tablet space, you can expect to see reference platforms built around Haswell to show OEMs exactly what they need to put down on a motherboard to deliver the sort of idle power consumption necessary to compete in the new world. It's not clear to me how Intel will enforce these guidelines, although it has a number of tools at its disposal - logo certification being the most obvious.
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Anand Lal Shimpi - Friday, October 5, 2012 - link
It's the other way around: not talking about Apple using Intel in iPads, but rather Apple ditching Intel in the MacBook Air.I do agree with Charlie in that there's a lot of pressure within Apple to move more designs away from Intel and to something home grown. I suspect what we'll see is the introduction of new ARM based form factors that might slowly shift revenue away from the traditional Macs rather than something as simple as dropping an Ax SoC in a MacBook Air.
Take care,
Anand
A5 - Friday, October 5, 2012 - link
Yeah. I knew what you were getting at, but I guess it wasn't that obvious for some people :-p.Something like an iPad 3 with an Apple-made keyboard case + some changes in iOS would make Intel and notebook OEMs really scared.
tipoo - Friday, October 5, 2012 - link
So pretty much the Surface tablet. The keyboard case looks amazing, can't wait to try one.Kevin G - Friday, October 5, 2012 - link
Apple is in the unique position that they could go with either platform way. They are capable of moving iOS to x86 or OS X to ARM on seemingly a whim. Their decision would be dictated not by current and chips arriving in the short term (Haswell and the Cortex A15) but rather long term road maps. Apple would be willing ditch their own CPU design if it brought a clear power, performance and process advantage from what they could do themselves. The reason why Apple manufactured an ARM chip themselves is that they couldn't get the power and performance out of SoC's from other companies.The message Intel wants to send to Apple is that Haswell (and then Broadwell) can compete in the ultra mobile market. Intel also knows the risk to them if Apple sticks to ARM: Apple is the dominate player in the tablet market and one of the major players in the cell phone market and pretty much the only success in the utlrabook segment. Apple's success is eating away the PC market which is Intel's bread and butter in x86 chip sales. So for the moment Intel is actively promoting Apple's competitors in the ultrabook segment and assist in 10W Ivy Bridge and 10W Haswell tablet designs.
If Intel can't get anyone to beat Apple, they might as well join them over the long run. This would also explain Intel toying with the idea of becoming a foundry. If Intel doesn't get their x86 chips into the iPad/iPhone, they might as well manufacture the ARM chips that do. Apple is also one of the few companies who would be willing to pay a premium for Intel foundry access (and the extra ARM not x86 premium).
So there are four scenarios that could play out in the long term: the status quo of x86 for OS X + ARM for iOS, x86 for both OS X + iOS, ARM for both OS X + iOS and ARM built by Intel for OS X + iOS.
Peanutsrevenge - Friday, October 5, 2012 - link
I will LMAO if Apple switch macs back to RISC in the next few years.Will be RISC, x86, RISC in the space of a decade.
Poor Crapple users having to keep swapping their software.
I laughed 6 ago, and I'll laugh again :D
Kevin G - Saturday, October 6, 2012 - link
But it wouldn't be the same RISC. ARM isn't PowerPC.And hey, Apple did go from CISC to RISC to back to CISC again for their Macs.
Penti - Saturday, October 6, 2012 - link
They hardly would want to be in the situation where they have to compete with Intel and Intel's performance again. Also their PC/Mac lineup is just so much smaller then the mobile market they have, why would they create teams of thousands of engineers (which they don't have) to create workstation processors for their mobile workstations and mac pro's? They couldn't really do that with PowerPC design despite having influence on chip architecture, they lost out in the race and just grows more dependent on other external suppliers and those Macs would loose the ability to run Boot camp'd or virtualized Windows. It's not the same x86 as it was in 2006 either.A switch would turn Macs into toys rather then creative and engineering tools. It would create an disadvantage with all the tools developed for x86 and if they drop high-end they might as well turn themselves into an mobile computing company and port their development tools to Windows. As it's not like they will replace all the client and server systems in the world or even aspire to.
I don't have anything against ARM creping into desktops. But they really has no reason to segment their system into ARM or x86. It's much easier to keep the iOS vs OS X divide.
Haswell will give you ARM or Atom (Z2760) battery life for just some hundred dollars more or so. If they can support the software better those machine will be loaded with software worth thousands of dollar per machine/user any way. Were the weaker machines simply can't run most of that. Casual users can still go with Atom if they want something weaker/cheaper or another ecosystem altogether.
Kevin G - Monday, October 8, 2012 - link
The market is less about performance now as even taking a few steps backward a user has a 'good enough' performance. It is about gaining mobility which is driven by reduction in power consumption.Would Apple want to compete with Intel's Xeon's line up? No and well, Apple isn't even trying to stay on the cutting edge there (their Mac Pro's are essentially a 3 year old design with moderate processor speed bumps in 2010 and 2012). If Apple was serious about performance here, they'd have a dual LGA 2011 Xeon as their flagship system. The creative and engineering types have been eager for such a system which Apple has effectively told them to look elsewhere for such a workstation.
With regards to virtualization, yes it would be a step backward not to be able to run x86 based VM's but ARM has defined their own VM extensions. So while OS X would lose the ability to host x86 based Windows VM's, their ARM hardware could native run OS X with an iOS guest, an Android guest or a Windows RT guest. There is also brute force emulation to get the job done if need be.
Moving to pure ARM is a valid path for iOS and OS X is a valid path for Apple though it is not their only long term option.
Penti - Tuesday, October 9, 2012 - link
You will not be able to license Windows RT at all as an end-user. Apple has no interest what so ever to support GNU/Linux based ARM-VMs.I'm sure they will update the Mac Pro the reason behind it is largely thanks to Intel themselves. That's not their only workstation though, and yes performance is important in the mobile (notebook space), performance per watt is really important too. If they want mobile workstations and engineering type machines they won't go with ARM. As it does mean they would have to compete with Intel. They could buy a firm with an x86 license and outdo Intel if they were really capable of that. ISA doesn't really matter here expect when it comes to tools.
baba264 - Friday, October 5, 2012 - link
"Within 8 years many expect all mainstream computing to move to smartphones, or whatever other ultra portable form factor computing device we're carrying around at that point."I don't know if I am in a minority or what, but I really don't see myself giving up my desktop anytime soon. I love my mechanical keyboard my large screen and my computing power. So I have to wander if I'm just an edge case or if analyst are reading too much in the rise of the smartphone.
Great article otherwise :).