The 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.

Platform Retargeting & Platform Power Other Power Savings & The Fourth Haswell
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  • dishayu - Friday, October 5, 2012 - link

    I derived immense pleasure reading the article. Thank you, Anand. Big ups for the comprehensive read.
    My thoughts :
    I think Intel really dropped the ball by not having unlinked clocks for each core, like qualcomm has for it's s4 pro processors. There are so many times that, for instance, i have a page open with some animated GIFs. They are strictly single thread processes and they won't let the processor go to idle state. And this is a very VERY common occurance that can IMO, only be solved by adopting unlocked states for each core. 3 cores can stay in sleep state (almost perpetually) and the processor runs on a single core with lowered frequency. THAT would be power efficient.
  • dagamer34 - Friday, October 5, 2012 - link

    Uhh... isn't turning off unused cores and overclocking the 4th core within TDP to perform single threaded tasks exactly what Turbo Boost introduced in Sandy Bridge is?
  • know of fence - Friday, October 5, 2012 - link

    Reducing power is great and also inevitable, but Intel's move to compete against everything and everybody is alarming. With everyone trying to follow/please Apple, that means nothing good for the consumer, throw-away luxury electronics for exceptionally well groomed masses.
    Also, isn't it too early to be hyping this stuff?
  • A5 - Friday, October 5, 2012 - link

    Intel has to compete against ARM to keep them from taking over the "good-enough" computing space.

    As for the rest of it, you're not making any sense.
  • jjj - Friday, October 5, 2012 - link

    The ARM problem is not about the product but about price, long term the CPU/SoC ASP will drop hard ,there is competition now. Servers will keep them on life support for a while but without fundamental changes to their business model they can't make it.
    Intel should remember how they won the market .
  • dishayu - Friday, October 5, 2012 - link

    It's about both. Intel does not have sufficinetly low power parts at all, regardless the price point.
  • mrdude - Friday, October 5, 2012 - link

    Regardless of whether they step foot into that end of the spectrum or not (and by Anand's analysis that's more likely with Broadwell and on?), they still need to compete on price.

    It's one thing to make a chip, it's quote another to make it competitive with respect to pricing. What works against a distant AMD won't work against ARM.
  • DesDizzy - Sunday, October 7, 2012 - link

    I agree. This seems to be something that most people overlook when addressing the Wintel monopoly. The costs of Wintel products are high within the PC/Laptop space. The price of ARM/Apps are cheap within the Smartphone/Tab space. How do Wintel square this circle without damaging their business model?
  • Krysto - Friday, October 5, 2012 - link

    You may not agree with Charlie, Anand, but reality seems to agree with him:

    http://www.techradar.com/news/computing/apple/appl...

    I really don't know how you can think Apple would ever start using Intel chips in their iPads when Apple has already proven they want to make their own chips with A6.

    Also, according to Charlie, Haswell will be like 40% more expensive than IVB. Atom tablets already seem to start at like $800. So I wish Intel good luck with that. Ultrabooks and Win8 hybrids won't drop down in price any time soon.

    http://semiaccurate.com/2012/10/03/oems-call-intel...
  • Penti - Friday, October 5, 2012 - link

    I don't know how you could fail so much in reading comprehension, Anand only said the same flying spaghetti monster-damn form factor. Nothing else. There also must be an ecosystem, but if you can run the same app on a tablet as well as a desktop on x86 with more performance then ARM why wouldn't you see vendors use it. It is a full system even capable of building itself. It's not about killing ARM. Intel still uses it, they need fairly high-performance RISC chips for stuff like baseband. They had a large markets in smart-phones before 2006 and they made the choice to sell it because they had Atom in their lineup. They didn't forget about it.

    It's Microsoft tablets that costs 500-900 dollars even on Atom, but they only need to compete with Windows RT which is totally retarded as far as corporate customers go and not the same system as 8 Pro, doesn't run the same software. An Android tablet could use a Z2460 (and coming Z2580, after that Valleyview SoC's) and build a 240 dollar tablet. There is no price difference to be had as far as hardware is concerned. Windows 8 tablets are a whole other form factor and device to begin with. Most will have keyboard and multitouch trackpad.

    He only talks about the same form factor, size and battery life here. In the Microsoft ecosystem there is really no reason to go to Windows RT powered ARM-devices which doesn't have better performance and runs no third party desktop (Win32/Full Windows SDK) software. It also lacks the same features in other areas which makes them devices instead of general computing platforms. Remember they offer both here. Hell the built in email is even worse then the one built into Android since version 3.0 or so, it's a lot worse then Third party mail-clients in Android, it's worse then mail-clients in Blackberry 10, Symbian, iOS and so on. If your replacing a desktop your not going with ARM here, not on a Windows device at least, Anand only talks about a new bread of DTR Tablets and Ultra-portables that will fit in the same form factor and battery life scenarios as ARM-tablets. Apple certainly don't need to participate here.

    Intel certainly has sales to be made if they move Haswell down to low-power Atom territory when it comes out later next year. They could be used as the only computing device you have (smartphone + hybrid tablet-pc). Replacing desktops, ARM/ATOM-tablets, media PCs for your TV (just stream with Miracast). Et cetera. ARM-devices would just be cheaper less capable devices there. But it's still different targets. Haswell still targets server (enterprise-market), desktop, notebooks with larger form-factor/power-usage, as well as more portable stuff. Atom is still for the handheld stuff you use with one hand. ARM has moved quiet fast but they have no reason to target high-performance applications or built 100W SoC's that is fast without parallel computing. Applications like high-performance routers for example still uses licensed and custom MIPS and PowerPC chips. There are plenty of markets where a full feature ARM Cortex or x86 won't work either. ARM is just moving into the multimedia-field, replacing customs architectures in TV's, displacing MIPS, PPC etc. If Apple builds a very large custom CPU-architecture compatible with ARM ISA for workstations, notebooks etc they will just be in the same position they were with PowerPC and have to compete with the high-performance chips that most can't compete with, even with much larger resources then Apple. Apple and Samsung has no reason in doing so outside handheld devices, low-power servers, consumer oriented routers, streaming media boxes which leaves plenty of room for Intel and all the rest. Plus WiFi and wireless baseband in a huge market in of it self and it doesn't matter what the application processor architecture is. Stuff like ARM has competed because you could replace previous products with it easily, thus taking some of the SoC-market away from other, but that coincides with the choice to do so.

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