Examining Intel’s New Speed Shift Tech on Skylake: More Responsive Processors
Modern computer processors are constantly changing their operating frequency (and voltage) depending on workload. For Intel processors, this is often handled by the operating system which will request a particular level of performance, known as the Performance State or P-State, from the processor. The processor then adjusts its frequencies and voltage levels to accomodate, in a DVFS (dynamic voltage and frequency scaling) sort of way, but only at the P-states fixed at the time of production. While the best for performance would be to run the system at the maximum all the time, due to the high voltage, this is the least efficient way to run a processor and wasteful in terms of energy used, which for mobile devices means a shorter battery life or thermal throttling. With the P-state model, to increase efficiency, the operating system can request lower P-states in order to save power, but if a task requires more performance, and the power/thermal budgets are sufficient, the P-State can be changed to accomodate. This ‘technology’ on Intel processors has historically been called ‘Speed Step’.
With Skylake, Intel’s newest 6th generation Core processors, this changes. The processor has been designed in a way that with the right commands, the OS can hand control of the frequency and voltage back to the processor. Intel is calling this technology ‘Speed Shift’. We’ve discussed Speed Shift before in Ian’s Skylake architecture analysis, but despite the in-depth talk from Intel, Speed Shift was noticably absent at the time of the launch of the processors. This is due to one of the requirements for Speed Shift — it requires operating system support to be able to hand over control of the processor performance to the CPU, and Intel had to work with Microsoft in order to get this functionality enabled in Windows 10. As of right now, anyone with a Skylake processor is actually not getting the benefit of the technology, at least right now. A patch will be rolled out in November for Windows 10 which will enable this functionality, but it is worth noting that it will take a while for it to roll out to new Windows 10 purchases.
Compared to Speed Step / P-state transitions, Intel’s new Speed Shift terminology, changes the game by having the operating system relinquish some or all control of the P-States, and handing that control off to the processor. This has a couple of noticable benefits. First, it is much faster for the processor to control the ramp up and down in frequency, compared to OS control. Second, the processor has much finer control over its states, allowing it to choose the most optimum performance level for a given task, and therefore using less energy as a result. Specific jumps in frequency are reduced to around 1ms with Speed Shift’s CPU control from 20-30 ms on OS control, and going from an efficient power state to maximum performance can be done in around 35 ms, compared to around 100 ms with the legacy implementation. As seen in the images below, neither technology can jump from low to high instantly, because to maintain data coherency through frequency/voltage changes there is an element of gradient as data is realigned.
The ability to quickly ramp up performance is done to increase overall responsiveness of the system, rather than linger at lower frequencies waiting for OS to pass commands through a translation layer. Speed Shift cannot increase absolute maximum performance, but on short workloads that require a brief burst of performance, it can make a big difference in how quickly that task gets done. Ultimately, much of what we do falls more into this category, such as web browsing or office work. As an example, web browsing is all about getting the page loaded quickly, and then getting the processor back down to idle.
For this short piece, Intel was able to provide us with the Windows 10 patch for Speed Shift ahead of time, so that we could test and see what kind of gains it can achieve. This gives us a somewhat unique situation, since we can isolate this one variable on a new processor and measure its impact on various workloads.
To test Speed Shift, I’ve chosen several tasks which have workloads that could show some gain from Speed Shift.
Tests which run the processor at its maximum frequency for long periods of time are not going to show any significant gain, since you are not limited by the responsiveness of the processor in those cases. The first test is PCMark 8, which is a benchmark which attempts to represent real-life tasks, and the workload is not constant. In addition, I’ve run the system through several Javascript tests, which are the best case scenario for something like Speed Shift, since the processor has to quickly complete a task in order to allow you to enjoy a website.
The processor in question is an Intel Core i7-6600U, with a base frequency of 2.6 GHz, and turbo frequency of 3.4 GHz. Despite the base frequency being rated on the box at 2.6 GHz, the processor can go all the way down to 400 Mhz when idle, so being able to ramp up quickly could make a big impact even on the U-series Skylake processors. My guess is that it will be even more beneficial to the Y series Core m3/m5/m7 parts since they have a larger dynamic range, and typically more thermal constraints.
PCMark 8
Both the Home and Work tests show a very small gain with Speed Shift enabled. The length of these benchmarks, which are between 30 and 50 minutes, would likely mask any gains on short workloads. I think this illustrates that Speed Shift is just one more tool, and not a holy grail for performance. The gain on Home is just under 3%, and the difference on the Work test is negligible.
JavaScript Tests
JavaScript is one of the use cases where short burst workloads are the name of the game, and here Speed Shift has a much bigger impact. All tests were done with the Microsoft Edge browser.
The time to complete the Kraken 1.1 test is the least affected, with just a 2.6% performance gain, but Octane’s scores shows over a 4% increase. The big win here though is WebXPRT. WebXPRT includes subtests, and in particular the Photo Enhancement subtest can see up to a 50% improvement in performance. This bumps the scores up significantly, with WebXPRT 2015 showing an almost 20% score increase, and WebXPRT 2013 has a 26% gain.
These leaps in performance are certainly the kind that would be noticeable to the end user manipulating photographs in something like Picasa or watching web-page based graph adjustments such as live stock feeds.
Power Consumption
The other side of the coin is power consumption. Having a processor that can quickly ramp up to its maximum frequency could mean that it will consume more power due to the greater penalty of increasing the voltage, but if it can complete the task quickly and get back to idle again, there is a chance to be more efficient when work is done in 10s of milliseconds rather than 100s of milliseconds, as the frequency ramps up and down again before the old P-state method has decided to do anything. The principle of ‘work fast, finish now’ was the backbone of Intel’s ‘Race To Sleep’ strategy during the ultrabook era and focused on the impulse of response-related performance, however the drive for battery life means that efficiency has tended to matter more, especially as devices and batteries get smaller.
Due to the way modern processors work, we don’t have the tools to directly measure the SoC power. Intel has told us that Speed Shift does not impact battery life very much, one way or the other, so to verify this, I’ve run our light battery life test with the option disabled and enabled.
This task is likely one of the best case scenarios for Speed Shift. It consists of launching four web pages per minute, with plenty of idle time in between. Although Speed Shift seems to have a slight edge, it is very small and would fall within the margin of error on this test. Some tasks may see a slight improvement in efficiency, and others may see a slight regression, but Speed Shift is less of a power savings tool than other pieces of Skylake. Looking at it another way, if, for example, the XPS 13 with Skylake was to get 15 hours of battery life, Speed Shift would only change the result by about 7 minutes. Responsiveness increases, but net power use remains about the same.
Final Words
With Skylake, while there was not the large leap in clock for clock performance gain that we have become accustomed to with new Intel microarchitectures, but when you look at the overall package, there was a decent net gain in performance combined with new technologies.
For example, being able to maintain higher Turbo frequencies on multiple cores has increased the stock to stock performance more than the smaller IPC gains.
Speed Shift is just one small part of the overall performance gain, and one that we have not been able to look at until now. It does lead to some pretty big gains in task completion, if the workloads are bursty and short enough for it to make a difference. It can’t increase the absolute performance of the processor, but it can get it to maximum performance in a much shorter amount of time, as well as get it back down to idle quicker. Intel is billing it as improved responsiveness, and it’s pretty clear that they have achieved that.
The one missing link is operating system support. We’ve been told that the patch to enable this is coming to Windows 10 in November. While this short piece looks at what Speed Shift can bring to the table in terms of performance, if you’d like to read more about how it is implemented, please check out the Skylake architecture analysis which goes into more detail.
Update: Daniel Rubino at Windows Central has tested the latest Windows 10 Insider build 10586 and it appears to enable Speed Shift on his Surface Pro 4, which is in-line with the November timeline we were provided.
Speed Shift v2: Speed Harder
by Ian Cutresson January 3, 2017 12:01 PM EST
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Intel Launches 7th Generation Kaby LakeA New Optimized 14nm Process: 14nm+Speed Shift v2: Speed HarderOptane Memory: Support for Intel 3D XPointIntel Authenticate and OPI 3.0The Kaby Lake-U/Y GPU — Media Capabilities200-Series Chipsets and MotherboardsA Brief Rundown of Results for Kaby Lake on Desktop
Speed Shift v2: Speed Harder
As originally reported at Kaby Lake-Y/U Launch
One of the new features for Skylake was Speed Shift.
With the right OS driver, the system could relinquish control of CPU turbo to the CPU itself. Using internal metric collection combined with access to system-level sensors, the CPU could adjust the frequency with more granularity and faster than the OS can. The purpose of Speed Shift was to allow the system to respond quicker to requests for performance (such as interacting with a touch screen or browsing the web), reduce delays and improve the user experience. So while the OS was limited to predefined P-state options, a Speed Shift enabled processor with the right driver had a near contiguous selection of CPU multipliers within a wide range to select from.
The first iteration of Speed Shift reduced the time for the CPU to hit peak frequencies from ~100 milliseconds down to around 30. The only limitation was the OS driver, which is now a part of Windows 10 and comes by default. We extensively tested the effects of the first iteration of Speed Shift at launch.
With Kaby Lake, the hardware control around Speed Shift has improved.
Intel isn’t technically giving this a new name, but it is an iterative update which I prefer to call ‘v2’, if only because the adjustment from v1 to v2 is big enough to note. There is no change in the OS driver, so the same Speed Shift driver works for both v1 and v2, but the performance means that a CPU can now reach peak frequency in 10-15 milliseconds rather than 30.
The light green and yellow lines show the difference between v1 and v2, with the yellow Kaby Lake processor getting up to 3.5 GHz incredibly quickly. This will have an impact on latency limited interactions as well as situations where delays occur, such as asynchronous web page loading. Speed Shift is a play for user experience, so I’m glad to see it is being worked on. We will obviously have to test this when we can.
A note about the graph, to explain why the lines seem to zig-zag between lower and higher frequencies because I have encountered this issue in the past. Intel’s test, as far as we were told, relies on detecting register counters that increment as instructions are processed.
By monitoring the value of these registers, the frequency can be extrapolated. Depending on the polling time, or adjacent point average (a common issue with counter based time benchmarks I’ve experienced academically), it can result it statistical variation depending on the capability of the code.
While this graph uses the i7-7500U, which was released back in September, Speed Shift v2 is a feature for all Kaby Lake processors in the stack with the right OS. We still have not received an official word if Intel is working closely with Apple to bring the feature to macOS, or even if it will be promoted if it ever makes the transition – Apple may never promote it so as not to confuse the non-technical media that follow Apple, but also not allow Intel to specify that Apple is using it. Or, it’ll be part of a presentation; we don’t know.
A New Optimized 14nm Process: 14nm+
Optane Memory: Support for Intel 3D XPoint
Intel Launches 7th Generation Kaby LakeA New Optimized 14nm Process: 14nm+Speed Shift v2: Speed HarderOptane Memory: Support for Intel 3D XPointIntel Authenticate and OPI 3.
0The Kaby Lake-U/Y GPU — Media Capabilities200-Series Chipsets and MotherboardsA Brief Rundown of Results for Kaby Lake on Desktop
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3DNews Technologies and IT market. News Electronics Development and Manufacturing Intel Activates New Control Technology The most interesting in the reviews
11/12/2015 [11:00], Alexey Stepin Speed Step processor dynamic frequency control technology is known to all owners of Intel solutions. But over the years since its introduction, this technology has already become obsolete — it does not differ in particular speed and does not always respond optimally to requests from the software, that is, to changes in the load on the CPU. Intel, of course, is aware of this and is working on improving the energy-saving technologies of new processors.
Speed Shift is indeed faster Recently, Intel has demonstrated a new technology for dynamically controlling processor cores called Speed Shift. According to the developer, Speed Shift responds much faster to increased CPU load and is generally more efficient than any version of Speed Step. The new technology works only on processors with the Skylake architecture, since part of it is inside the processor itself and is implemented in hardware. Another limitation is on the part of the operating system — only Windows 10 is currently supported. The corresponding update will be released during this month. Advantages of Speed Shift compared to the previous technology
Both technologies use the so-called P-state, modes with a certain frequency and voltage, the parameters of which are set in the BIOS of the system and are controlled by the operating system in the Speed Step implementation. Speed Shift has almost no effect on the performance level The introduction of Speed Shift does not mean an increase in the number of instructions executed per clock and a general increase in performance should not be expected, because there are no new execution units in the processor at the hardware level. This is confirmed by tests conducted by our foreign colleagues from the AnandTech resource. But new technology for dynamically managing processor core frequencies and voltages improves the comfort level of tasks that often require short bursts of increased performance. Such tasks include, for example, the use of modern browsers. Source:
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The first results have already been presented, and they look impressive. 
In Speed Shift, mode control can be fully or partially assigned to the internal logic of the processor, which significantly reduces delays. If the old implementation usually responds within 20‒30 milliseconds, then in Speed Shift the response time can reach 1 millisecond. The speed of the processor from the minimum to full power has also increased, from 100 to 35 milliseconds. 
Any software that by its nature likes to frequently «play» P-state modes will perform better and be more responsive with the introduction of Intel Speed Shift. Speed Shift technology.
Speed Shift technology.
The design of Skylake processors was strongly influenced by the desire
to energy savings. Here, both traditional approaches have been developed,
as well as some fundamentally new ideas.
Processor design now does not include
integrated power converter (it was removed precisely for reasons
efficiency — in the most energy-efficient CPUs with a thermal package of about 4.5
W). In future microarchitectures, Intel is going to return the converter again
back to the processor, but not in all versions of the design, but only in those that
designed for fairly liberal thermal packages.
Intel engineers broke the processor into more,
than before, the number of energy domains capable of independently disconnecting from
power lines in case of inactivity. Now it has come even to individual
executive devices. Skylake can be independently de-energized in case of
idle even 256-bit execution units responsible for execution
AVX2-command.
Similar technologies in one form or another
been used for a very long time, but Skylake has a really revolutionary
innovation — Speed Shift technology ,
the essence of which lies in the fact that the processor is now given a much larger
freedom of action in managing their own energy-saving states.
In general, modern processors can
independently, that is, without the participation of the operating system, switch its
frequency between nominal and turbo. However, the transition to
economical states with reduced voltages and frequencies requires
direct participation of the OS. It is she who gives the commands to reduce frequencies,
having previously turned to the firmware and found out which modes with
reduced power consumption can offer a specific instance of the CPU. IN
as a result, switching to any economical state is a whole complex of measures,
which takes a lot of time. Even worse is the situation with the exit from such
modes. The processor must inform the operating system that
something happened, then the system must process this information and transmit
processor a command to switch the frequency — such a chain of actions takes up to
30 ms.
Implementation same speed
Shift gives the processor greater independence , it retains its subordination to the operating system,
which can transfer it to a lower frequency, for example, to save
energy in a running out battery of a mobile device.
But routine questions
switching power-saving states processor
now takes over completely, which significantly improves reaction time and
allows you to enter and exit power-saving modes for units of milliseconds. Reduction
reaction time to changing conditions should, on the one hand, serve the purpose
energy savings, and on the other hand, it can positively affect
performance. In other words, Skylake processors with Intel Speed Shift technology will be able to independently select
the most appropriate frequency of operation based on the load placed on them,
moreover, the switching of states will occur more accurately and more quickly.
Speed Shift technology takes into account one more
aspect. Reducing the frequency to reduce power consumption does not always give
expected effect. The problem is that as the frequency decreases below a certain
limit value, consumption begins to fall to a much lesser extent due to
gaining more influence currents
leaks .
Therefore, in some energy-saving modes, it is more efficient
it turns out to raise the processor frequency, quickly execute the necessary code, and
then put the processor into sleep mode. This strategy is used in Skylake,
where special algorithms are introduced, capable of deep energy-saving
states periodically send the processor to sleep and then wake up
its for solving current low priority
tasks .
Speed Shift Technology, for its operation,
support from the operating system is required (it can only be provided by
Windows 10). All other OCs, including all sorts of variations of Linux or
Android, support for Speed Shift is not yet provided. Of course, over time, this
the problem will be solved one way or another.
Intel is also working on the development of processor
blocks with fixed functions, which also save energy. For example,
video encoding and decoding through Quick Sync capabilities rather than
processor cores, also provides a good opportunity for energy saving.