Intel arms its Core i5 and Core i7 CPUs with Turbo Boost. AMD's
hexa-core Phenom II X6 chips sport Turbo CORE. Both technologies
dynamically increase performance based on perceived workloads and
available thermal headroom. Which one does the better job?
Automotive
turbochargers increase torque and power output, which is why they're
used to increase the air-fuel mixture rate per combustion cycle. AMD’s
and Intel’s performance-improving technologies don't actually a require
an additional piece of hardware bolted on like a turbo would be, but
they both invoke the gas compressor namesake anyway.
Instead, both companies' latest six-core models dynamically increase
their clock rates to deliver better performance under workload
conditions that allow for faster frequencies. We wanted to see whether
Intel's Turbo Boost or AMD's Turbo CORE is the better implementation.
Intel was first to offer this performance-enhancing feature. Its Nehalem
architecture and the Core i7-900 family first introduced Turbo Boost in
late 2008. The technology is capable of accelerating all cores by one
clock speed bin (133 MHz) and one or two cores by two speed increments
(depending on the particular model). In 2009, the Lynnfield Core i5/i7
quad-core processors for LGA 1156 enabled a more advanced implementation
able to accelerate one or two cores by four clock speed increments. The
800-series even bumps clock speed up by five clock speed bins for a
single core. One speed bin equals 133 MHz at stock speed, so we’re
effectively talking about a 133 to 533 MHz dynamic increase. Turbo Boost
is also an available feature on the Clarkdale-based Core i5 dual-core
chips.
AMD introduced Turbo CORE with its six-core Phenom II X6 and will keep
adding the feature to new models. While Intel's implementation allows
the CPU to specifically accelerate one or more cores, AMD’s approach
only accelerates three cores in the case of a six-core CPU and only two
with quad-core processors.
We grabbed the latest AMD Phenom II X6 and Core i7-980X six-core
processors to find out which implementation works best across our
benchmark suite in terms of performance and power efficiency. Since the
performance level of these two chips is rather different—Intel has more
punch—we decided to compare benchmark results with and without the Turbo
feature and normalize these to 100% for the non-Turbo results. This way
we can compare the relative impact on the respective configurations
despite the absolute performance difference. In short, which Turbo
implementation gives you more bang for the buck?
Turbo CORE is available on all AMD Phenom II X4 and X6 processors based
on the recent 45 nm designs, namely the Thuban six-core and
seen-in-the-wild but not-yet-available-at-retail Zosma quad-core
models. Should it ever see retail availability, the Phenom II X4 960T at
3.0 GHz nominal speed could accelerate two cores up to 3.4 GHz (+400
MHz) with the thermal headroom available, and if the application load
demands the increase. The Phenom II X6 processors increase their clock
speeds by 500 MHz, with the exception of the 1090T flagship, which adds
400 MHz to reach from 3.2 to 3.6 GHz.
This implementation can be considered an addition to the Cool’n’Quiet
feature, which reduces clock speeds and voltages if there is little work
for the processor to do. Once half of the cores are idle, the system
reduces their clock speed to the Cool’n’Quiet minimum of 800 MHz. The
next step is a voltage increase for the remaining active cores paired
with a speed lift of up to 500 MHz, as explained above.
Unfortunately, few workloads would tax exactly three cores by 100%—the
conditions needed for AMD’s solution to run at 3.6 GHz. We found that a
two-core load scenario is more realistic. This is why the feature works
better on a CPU with an even core count, such as the Phenom II X4 960T.
AMD’s Turbo CORE control allows Black Edition processor users to adjust
their number of accelerated cores. This makes analysis more complex, but
also gives enthusiasts a more powerful tool for fine tuning their
systems.
Intel's implementation works best on processors with a lot of
scalability inherent to their design, as Turbo Boost covers much broader
clock speed ranges. For example, the new six-core "Gulftown," Core
i7-980X, is already running close to its thermal ceiling under load.
Thus, it's limited to a 266 MHz boost with a single core active, and a
modest 133 MHz bump when two or more cores are active. Knowing that
Intel’s overclocking headroom is sizable, this is really a pity for
enthusiasts. After all, the Phenom II X6 can speed up three cores by up
to 400 MHz using a 45 nm process.
Intel’s power gate transistors facilitate cutting power to individual
cores. This allows the processor to actually disengage those cores from
the overall power envelope, consequently "buying" the overhead needed to
increase the remaining cores’ clock speed. The premise here is that
fewer cores can run at higher clock speeds before they reach the same
thermal output.
While AMD basically reduces clock speed and voltage for inactive cores,
Intel can physically shut them down. In theory, this should result in
lower power consumption and, paired with the ability to dynamically
scale one or more cores up or down, a better overall performance result.
Intel has another advantage that should be mentioned. While AMD's
six-core processors access 6 MB of shared L3 cache, Intel's architecture
currently offers a massive 12 MB repository. If you switch off
individual cores, the remaining active processing units can still access
the full 12 MB L3. This should provide advantages for applications that
work with limited data and use few threads.
3DMark, a synthetic benchmark, realizes a slight advantage from Intel's architecture and Turbo Boost.
PCMark Vantage clearly shows that Intel’s approach delivers performance
gains while AMD’s Turbo Core doesn’t seem to help as much.
iTunes is single-threaded, and is better-accelerated on the Phenom II X6 with Turbo CORE enabled.
The same applies to Lame.
MainConcept is optimized to take advantage of multiple cores, so it
benefits more from Turbo Boost, which can kick in even if many cores are
taxed.
Once again, we see the multi-threaded advantage in HandBrake, where
AMD's processor easily hits its limits on all six cores, preventing
Turbo CORE from kicking in.
As expected, switching the Turbo features on or off doesn’t change idle power.
However, peak power increases under Turbo Boost and Turbo CORE. The differences are small, though.
The runtime for our full efficiency suite decreases a bit more on the
Intel platform, as there are more applications taking advantage of
Intel’s Turbo Boost implementation than AMD’s Turbo CORE.
Average power consumption is much higher on the AMD system with Turbo CORE enabled.
The total power used is exactly the same on the Intel system. This is
interesting because the Core i7-980X with Turbo Boost is still faster.
AMD’s Turbo CORE-enabled Phenom II X6 delivers more performance, but it
requires more power to deliver it.
In the end, the Intel chip's efficiency stays constant. The total power
used is exactly the same, but the average power is higher during the
workload. As a result, the efficiency is identical. This is like
reaching your destination faster in a car without changing your mileage
per gallon. AMD’s Turbo implementation sacrifices power efficiency.
Runtime decreases, but average power and total power used increase at a
higher proportion.
We can only recommend that AMD and Intel continue implementing and
developing their Turbo-oriented features. Both do their job in
increasing performance. Since the two approaches are different, though,
we found that their outcomes in real life are different, as well.
Let’s start with Intel. The six-core, 3.2 GHz Core i7-980X speeds up a
single core by 266 MHz if a single-threaded application wants maximum
performance, and it can accelerate all six cores by 133 MHz if thermal
headroom allows. This is the main difference compared to AMD’s solution,
because Intel's Gulftown design can accelerate single-threaded apps, as
well as high-end applications. From a multi-core processing standpoint,
Turbo Boost makes more sense than Turbo CORE, since all types of
workload benefit when compared to nominal clock speed.
AMD’s Turbo CORE only knows one acceleration mode. It increases clock
speed for three cores by up to 400 MHz in the case of the Phenom II X6
1090T 3.2 GHz six-core. This means that all applications that utilize no
more than three cores experience immediate acceleration. In this case,
we found that AMD's performance improvement is higher, as a 400 MHz
upgrade is much more noticeable than Intel’s 133/266 MHz speed bump. The
downside is nonexistent acceleration if four to six cores are being
taxed.
Neither solution is a clear winner. Intel is better for extremely
performance-hungry, multi-threaded environments, while AMD's approach
provides more benefits for less-threaded environments. The best Turbo
technology would be a more granular one, and a perfect Turbo mode would
accelerate a single core by even more than AMD’s 400 MHz, two cores by
around 400 MHz, three and four cores by less, and all cores by as much
as the remaining thermal envelope allows.
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