nedoflagman / Processors and memory


The announcement of high-performance multi-core processors Broadwell-E was primarily interesting for enthusiasts engaged in multi-threaded computing. Intel decided to bring older Core i7 together with Xeon processors for workstations, resulting in a top CPU for desktops, which received ten cores. With a strong emphasis on this side of Broadwell-E and the entire past announcement was built. Which, incidentally, is not so surprising: no other special improvements in the Broadwell-E design have appeared, and the Broadwell microarchitecture is neither new nor noticeable superior to Haswell. As a result, most of the reviews that can be read about the new solutions for the LGA2011-v3 platform concern only the ten-core flagship – Core i7-6950X Extreme Edition.

At the same time, it’s hardly possible to call the Core i7-6950X the most popular processor among the new products. Yes, ten computing cores is a huge and even unprecedented power by the standards of desktop systems, but the cost of a processor with such an arsenal, installed by a microprocessor giant at $ 1,723, goes beyond all reasonable limits. In other words, testing such a processor is really interesting from the standpoint of theory, but in practice it is much more important, as is the case with the performance of more accessible options. Unfortunately, Intel refused to provide us with additional Broadwell-E samples for the study. But our long-time partner, Regard company, came to the rescue, in the warehouse of which the necessary processors were found. Thanks to this, today we have the opportunity to continue the conversation about updating the LGA2011-v3 platform and to get acquainted with the second representative in the Broadwell-E family – the Core i7-6900K processor.

Core i7-6950X Core i7-6900K Core i7-6850K Core i7-6800K
Core / Threads 10/20 8/16 6/12 6/12
The clock speed, GHz 3.0 3,2 3.6 3,4
Max. frequency in turbo mode, GHz 4.0 4.0 4.0 3.8
Support for the Turbo Boost Max 3.0 There are There are There are There are
Unlocked multipliers There are There are There are There are
L3-cache, Mbyte 25 20 15 15
The number of PCI Express 3.0 lines 40 40 40 28
Memory 4 channels
DDR4-2400
4 channels
DDR4-2400
4 channels
DDR4-2400
4 channels
DDR4-2400
TDP, W 140 140 140 140
The processor socket LGA2011-v3 LGA2011-v3 LGA2011-v3 LGA2011-v3
The price is $ 1,723 $ 1,089 $ 617 $ 434

Yes, the Core i7-6900K is not a 10-core, but it’s also a very respectable model, with an array of eight cores supporting Hyper-Threading technology. It deserves special attention because, based on the characteristics, the Core i7-6900K is a modern replacement for the past flagship from the Haswell-E generation, the Core i7-5960X. Moreover, the number of cores coincides with these processors but the cost is similar to – they are both estimated in an amount close to $ 1,000, with which enthusiasts of high productivity can be said to have already grown accustomed.

⇡ # Core i7-6900K: details

To begin the story about any consumer processors in LGA2011-v3-performance follows with a reminder that in reality this desktop platform is not so much an independent branch of development as an adapted version of the server platform. In the desktop version, multiprocessor configurations are not supported and there is no compatibility with the register memory, but otherwise very close parallels can be drawn between Broadwell-E and the younger versions of the Broadwell-EP series processors. Up to the point that all Core i7 for LGA2011-v3 are based on the same semiconductor chip as Xeon E5 v4 processors with a maximum of eight cores

So do not be surprised that while mass processors have long moved to the Skylake microarchitecture, the new high-performance solutions are based on the micro-architecture of the previous generation – Broadwell. This is primarily due to the fact that Intel’s server clients require stability and support of the platform’s relevance for a longer time than is accepted in desktops, as a result of which development in this area is somewhat slowed down. But you can be completely confident in protecting your investments: for at least the next year Broadwell-E will remain the fastest Intel offer for a PC.

The fact that the microarchitecture Skylake did not get into high-performance processors for enthusiasts, in fact, there is no catastrophe. On the contrary, it is thanks to this that the old platform LGA2011-v3 and the set of system logic Intel X99, presented in the summer of 2014, retained full compatibility with the novelties. Yes, motherboard manufacturers saw Broadwell-E as an excellent opportunity to upgrade their products, but the old boards introduced with Haswell-E are also capable of working with processors like Core i7-6900K after firmware upgrade. As for the level of performance, the microarchitecture of Skylake is more effective than Broadwell is not too noticeable, and it is quite possible to say that enthusiasts do not lose much here. This is also the case with other consumer characteristics, because the transition to a 14-nm process technology, which could significantly affect energy efficiency and frequency potential, took place just in the Broadwell generation.

Everything said is true for both Core i7-6950X, which passed through our lab a little earlier, and for the Core i7-6900K considered in this review. After all, these two processors differ only in the number of cores and clock frequencies. They are based on the same semiconductor crystal LCC with the only difference that in the eight-core version, two cores and two cache blocks are turned off, therefore the capacity of its third-level cache memory is not 25 but 20 MB.

But in comparison with the Core i7-5960X of Haswell-E generation, the new Core i7-6900K looks quite advantageous. Of course, it can not be said that there is a significant difference between the Haswell and Broadwell microarchitecture in terms of specific performance. And moreover, for most of the characteristics – the number of computing cores, the size of the cache, the number of PCI Express lines, the structure of the memory subsystem, the calculated heat dissipation, and so on. – there is no difference between these representatives of Haswell-E and Broadwell-E families. But the Broadwell technology process with 14-nm standards and three-dimensional transistors of the second generation is something that means something. For example, it allows you to raise clock frequencies without affecting the boundaries of the heat packet.

Core i7-6900K Core i7-5960 X ] Code name / architecture Broadwell-E Haswell-E The technology of production 14 nm 22 nm Release date Q2’16 Q3’14 Kernels / streams 8/16 6/12 The clock speed 3.2 GHz 3.0 GHz Max. frequency in turbo mode 4.0 GHz 3.5 GHz Support for the Turbo Boost Max 3.0 There are No Unlocked multipliers There are There are L3-cache 20MB 20MB The number of PCI Express 3.0 lines 40 40 Memory 4 channels DDR4-2400 4 channels DDR4-2133 TDP 140 W 140 W The processor socket LGA2011-v3 LGA2011-v3 The price is $ 1,089 $ 999

As you can see from the table below, the frequencies of the eight-core processor Core i7-6900K became 200 MHz higher than those of the Core i7-5960X, and reached the values ​​typical for Haswell-E’s six-core processors. In addition, do not forget about the new technology Turbo Boost Max 3.0, which can output one of the Core i7-6900K cores (as in other Broadwell-E) at a frequency of 4.0 GHz.

Representatives of the Broadwell-E family can boast of one more improvement – an improved four-channel memory controller. From a formal point of view, this means that the Core i7-6900K processor has officially supported the DDR4-2400 standard and compatibility with 16GB modules. But in fact, the memory controller also received more flexible settings in terms of selecting modes, as well as the ability to overclock DDR4 SDRAM to higher frequencies than before. In particular, the maximum memory frequency that can be installed in the LGA2011-v3-system based on the Core i7-6900K without increasing the BCLK frequency, now reaches 4000 MHz.

The official price of the Core i7-6900K is $ 1,089. This is $ 90 more expensive than the cost and is worth the Core i7-5960X, but it’s as much as $ 634 less than Intel asks for the 10-core flagship of the Core i7-6950X. As a result, the Core i7-6900K looks better in the Broadwell-E lineup than the older offer: it is 37 percent cheaper, given that the number of cores it offers is less than 20 percent.

However, Intel still positions the Core i7-6900K as a slightly higher processor than the Core i7-5960X from the previous generation. But a more perfect microarchitecture hardly played any role at the same time. Yes, in Broadwell, branch prediction algorithms have been improved and the main internal buffers have been enlarged, plus faster execution patterns for multiplying and dividing instructions have been added. However, all this gives only a ridiculous 3% increase in specific productivity. Therefore, the superiority of the Core i7-6900K is determined primarily by its frequencies. And this should be discussed in more detail.

⇡ # Core i7-6900K: clock speed and Turbo Boost Max 3.0

Formally, the nominal clock speed of the Core i7-6900K is set at 3.2 GHz. However, in practice at maximum load this processor operates at a frequency of 3.5 GHz. This is affected by the support of this processor technology Turbo Boost 2.0, which increases the frequency by several steps in the event that there are no obvious contra-indications from the temperature regime.

CPU-Z screenshot displays a typical state of the Core i7-6900K: 3.5 GHz frequency with a supply voltage of about 1.1 V.

Technology Turbo Boost 2.0 under certain conditions allows the processor to accelerate and stronger. If only one or two kernels of the eight-core processor are used by the work, and the remaining cores are in an idle state, the frequency can be dynamically increased to 3.7 GHz.

Note that the voltage also increases with the frequency, but since the high load affects only one or two cores, the processor certainly remains within the established 140-watt heat package.

I must say that the technology Turbo Boost 2.0 similarly worked and the Core i7-5960X. The difference is in fact only in specific frequencies – a newer 14-nm Core i7-6900K chip in any state faster at 200 MHz. And such a six percent increase in frequency could hardly have become a serious argument in favor of the novelty, but it is not the only thing that matters to them. On the usual technology Turbo Boost 2.0, Intel developers have made an even more powerful forced turbo mode – Turbo Boost Max 3.0 technology.

The essence of Turbo Boost Max 3.0 is that with a single-threaded load, the processor is allowed to output to an even higher frequency – 4.0 GHz. However, such automatic overclocking could not be implemented within Turbo Boost 2.0, because it is not allowed for the whole processor, but only for one particular core. To realize such an enhanced turbo mode, Intel in the production process reveals on the semiconductor crystal the most compliant in the frequency plan core and marks it in a special way, allowing it to increase its frequency more significantly than for all other cores. And when the load falls on this particular core, and the remaining CPU cores are idle, the frequency within Turbo Boost Max 3.0 rises to 4.0 GHz.

In other words, Turbo Boost Max 3.0 is fundamentally different from Turbo Boost 2.0 at least because this solution is tightly tied to one specially selected processor core. Therefore, the proper functioning of this technology requires additional support from the operating system, which should understand that one of the cores in Broadwell-E is better than the others, and carry the entire single-threaded load to it. Unfortunately, current OS versions do not work that way, and Turbo Boost Max 3.0 needs to use an additional driver offered by Intel.

It should be noted that at the moment this driver can not be called an exhaustive solution, but there is simply no alternative – for the operating system, all the cores are always equal. The problem with the driver is that it checks the load only at certain intervals (by default – once a second) and transfers to the fast core only those processes that take away more than 90 percent of the resources of one core. In other words, while this is more like a kind of “crutch”, since the driver obviously lacks a closer integration with the task manager. However, with time, native support for Turbo Boost Max 3.0 will certainly be added to the current version of Windows via the update system.

In addition, the correct operation of Turbo Boost Max 3.0 also depends on the motherboard BIOS, in which the independent control of processor core multipliers must be correctly implemented. In theory, the third version of the turbo mode is a superstructure over the second version. That is, Turbo Boost Max 3.0 does not cancel Turbo Boost 2.0, but only adds another faster mode, which is activated exclusively with a single-threaded load. In fact, the motherboard manufacturers can interpret Turbo Boost Max 3.0 more freely. For example, during our first acquaintance with the Core i7-6950X processor, the test motherboard ASUS X99-Deluxe, with the inclusion of a new autodiscovery technology regardless of the load, further increased the speed of all CPU cores, and this should not be. Fortunately, in the new firmware updates the situation is fixed, and now Turbo Boost Max 3.0 on our test platform functions exactly as it should.

As for the Core i7-6900K, the canonical version of Turbo Boost Max 3.0 for it should look like this:

As you can see, the single-threaded load was transferred to Core7 core (it turned out to be the most successful for our Core i7-6900K), and its frequency was increased to 4.0 GHz. At the same time, the processor voltage is increased to a very high value – 1,243 V. Such a serious overvaluation should become a guarantee of stability of the CPU. But the processor remains within the thermal package as due to the fact that the rest of the cores do not work, and thanks to the special “success” of Core7.

It turns out that with the introduction of Turbo Boost Max 3.0, Intel squeezed out Broadwell-E the last frequency potential that these processors can offer within the established boundaries of heat generation and power consumption. And the inability to achieve 4 GHz within the old Turbo Boost 2.0 technology only underlines this. Just think: for the processor to work with a single-threaded load with this frequency, it is necessary specifically to choose the best core of eight!

⇡ # Dispersal

Studying the overclocking potential of the older Broadwell-E, Core i7-6950X, was at one time a cause for disappointment. It was completely overclocked only to 3.9 GHz, and in order to squeeze at least 4.3 GHz from this processor, we had to slow down significantly when executing AVX-instructions, which could not but strike at real performance. However, the modest frequency potential of the Core i7-6950X could be attributed to its radical multi-core. There is no doubt that ten computing cores working simultaneously can generate a lot of heat, which naturally creates significant obstacles to the conquest of high clock frequencies.

Another thing is a simpler Core i7-6900K, which has two fewer cores. With it overclocking can go more fun, besides the practical overclocking experience of such a processor can be compared with the results of the overclocking of the eight-core Core i7-5960X, which we were able to bring to the 4.2 GHz mark without any doubtful tweaks.

However, it is not worthwhile to pin high hopes on the Core i7-6900K. По сравнению с Core i7-5960X он перешёл на более современный техпроцесс с 14-нм нормами, и на самом деле это вряд ли стоит считать явным плюсом. Практика подсказывает, что новые производственные технологии уже давно не обеспечивают увеличения частотного потенциала. Более того, процессоры Broadwell-C в LGA1150-исполнении, с которыми нам довелось познакомиться прошлым летом, оказались с точки зрения оверклокинга наихудшими предложениями Intel за последние несколько лет. Конечно, с тех пор прошло немало времени, и Intel вполне могла отшлифовать свой передовой техпроцесс, но в случае с Broadwell-E дело осложняется ещё и тем, что площадь полупроводникового кристалла по сравнению с Haswell-E уменьшилась примерно на 30 процентов, и это закономерно увеличивает плотность теплового потока, от которого необходимо избавляться при работе процессора в ресурсоёмких задачах. И пусть в Core i7-6900K, как и в других LGA2011-v3-процессорах последнего поколения, в качестве внутреннего термоинтерфейса используется припой на основе индия, никаких гарантий высокого разгона это не даёт.

Результаты натурного эксперимента по разгону Core i7-6900K подтвердили все изложенные выше опасения. Его беспроблемного функционирования без перегрева нам удалось добиться лишь при максимальной частоте 4,0 ГГц.

Как видно по приведённому скриншоту, для проверки стабильности мы использовали утилиту LinX 0.6.8. Для охлаждения же процессора использовался традиционный двухбашенный воздушный кулер Noctua NH-D15.

Работа Core i7-6900K на частоте 4,0 ГГц потребовала повышения его напряжения питания до 1,2 В, но температура в таком состоянии во время прохождения теста на стабильность не превышала 93 градусов. Это – вполне приемлемый режим в том числе и для долговременной эксплуатации, так как троттлинг у Broadwell-E включается при 100-градусной температуре.

Однако разгон до 4,0 ГГц, честно говоря, каким-то солидным достижением совсем не кажется. Мало того, что Core i7-5960X разгонялся лучше, к тому же и частота 4,0 ГГц для Core i7-6900K– это номинальный потолок для технологии Turbo Boost Max 3.0. То есть, по большому счёту, наш разгон лучше официального турборежима лишь тем, что он позволяет держать 4-гигагерцевую частоту в том числе и при многопоточной нагрузке. То есть все высказанные опасения подтвердились: в оверклокинге Core i7-6900K проигрывает своему предшественнику, Core i7-5960X.

Впрочем, не следует забывать о том, что процессоры поколения Broadwell-E приобрели новые оверклокерские возможности, например большую гибкость настроек множителей. Они не только позволяют устанавливать различную частоту для разных ядер, но и умеют сбрасывать свою скорость на AVX-операциях, которые провоцируют наиболее сильные выбросы тепла, вызывающие критический перегрев процессора. Так, воспользовавшись этой возможностью и заметно срезав производительность векторных команд, в прошлом тестировании Broadwell-E мы смогли довести частоту десятиядерника Core i7-6950X до 4,3 ГГц. Однако такой подход хорош лишь для формального разгона, а не для повседневной работы. На практике высокопроизводительные LGA2011-v3-системы нередко имеют дело с ресурсоёмкими приложениями для создания и обработки контента, а в таких задачах AVX-инструкции применяются очень часто. Поэтому на этот раз мы решили постараться обойтись без чрезмерного затормаживания процессора на векторной нагрузке. Вместо этого мы предприняли попытку дополнительно разогнать Core i7-6900K выше 4-гигагерцевой границы, зафиксировав его частоту при работе с AVX-инструкциями на уже достигнутом рубеже.

Однако не слишком вдохновляющие результаты принёс и такой подход. Стабильность при нагрузке, свободной от AVX-команд, с напряжением Vcore, равным 1,2 В, оказалась достижима лишь при частоте 4,1 ГГц. Больший разгон требовал дополнительной прибавки к напряжению питания, но она, в свою очередь, приводила к перегреву процессора под AVX-нагрузкой на частоте 4,0 ГГц.

В результате нам пришлось смириться с тем, что предел разгона Core i7-6900K с использованием производительного воздушного охлаждения находится в окрестности 4 ГГц и представители семейства Broadwell-E в оверклокинге проявляют себя хуже, чем Haswell-E. Что же касается нашего экземпляра, то на комбинированной частоте 4,0-4,1 ГГц (в зависимости от AVX-нагрузки) он продемонстрировал свою полную работоспособность, и в тестах производительности вы найдёте его показатели в таком режиме.

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