desktop Carrizo / processors and memory


Hybrid processors of the Kaveri family remain the main offer of AMD for desktop personal computers for over two years now. AMD threw the main forces on the development of promising microarchitecture Zen, and therefore tries to reduce its costs, if possible, in connection with the preparation of any new products with different incarnations of the Bulldozer design. So, the planned update of the lineup of desktop processors performed by Socket FM2 + this spring did not bring any fundamental changes. Actually AMD only slightly increased the clock frequencies of APUs familiar to us, based on the processor micro-architecture of Steamroller and having graphics cores of the GCN 1.2 family. And this means that all models of AMD’s hybrid desktop processors announced during February March are again familiar to us Kaveri (or, if you will, Godavari).

Of course, such a slowdown in progress is hardly a reason for pride. Especially on the background of the fact that Steamroller – far from the most recent microarchitecture in the arsenal of AMD. The fact is that mobile systems in the middle of last year still received the attention of engineers: for them something new was proposed – the Carrizo processors on the improved microarchitecture Excavator. But symmetric offers for desktops were not planned at all. Design Carrizo received a clear focus on energy efficiency, and therefore use it in models for the Socket FM2 + platform without a serious modification of AMD considered inappropriate. As a result, mobile processors have moved forward somewhat compared to their desktop counterparts, but, by and large, this is of little concern, because any AMD solutions with Bulldozer microarchitectures are certainly inferior to the current Intel offers in everything except the performance of the graphics core.

However, all this does not mean that the microarchitecture Excavator will pass by the desktop segment. The first “transitional” processors for the Socket AM4 platform, which in the future will have to become a typical habitat for APU and CPU based on the fundamentally new design of Zen, will be based on the Excavator base. Bristol Ridge products will be brought to the desktop segment in the second half of this year, which, in addition to Excavator cores, will also be able to offer integrated GCN 1.2 graphics and a memory controller supporting DDR4 SDRAM.

However, AMD would not be itself, if in the initial rather harmonious and logical plan along the way would not begin to make changes. One of these changes was the recent appearance of an unexpected model with Carrizo design among the desktop processors for Socket FM2 + based on Kaveri. This unexpected newcomer was the Athlon X4 845, which, formally speaking, the APU is not even, but a processor without a graphics core. Nevertheless, this new product looks even more interesting. After all, in the end, the Athlon X4 845 is not only the exclusive carrier of the Excavator microarchitecture in the desktop segment, but also the cheapest desktop chip, capable of offering four almost full-fledged computing cores. Such an original and seductive product simply could not be bypassed by the attention of our laboratory, and therefore it was awarded a separate review.

But even more significant factor, heating interest to Athlon X4 845, is that this processor gives an opportunity to estimate in advance what can be expected from Bristol Ridge in terms of computing performance. In addition, the originality of this product is also intriguing. Despite the fact that the Athlon X4 845 is based on the most modern version of the Bulldozer microarchitecture, he entered the Socket FM2 + processor lineup not from above, but from below, acting as a budget and energy efficient solution. This is explained in part by the fact that we are dealing with a processor that has become a desktop willy-nilly: in fact, under the name Athlon X4 845, the manufacturer implements semiconductor crystals Carrizo, which either have an inoperative graphics core, or are unable to fit into mobile thermal packets of 15-35 watts. That is, speaking in a simple way, Athlon X4 845 is a rough desktop adaptation of a laptop chip. But is it appropriate for such a processor in the product line for desktops? Let’s figure it out.

⇡ # Athlon X4 845 in detail

At first glance, the characteristics of the Athlon X4 845 look quite familiar. It’s not for nothing that AMD placed this processor in the old Athlon X4 line, which includes quad-core processors without a graphics core in the Socket FM2 + version. However, the true essence of the Athlon X4 845 is Carrizo – it is easy to see at a closer look and, for example, is clearly visible in any diagnostic program.

The Athlon X4 845 is based on two dual-core dozer modules with the Excavator microarchitecture. The differences compared to the previous one, which is well known to us by Kaveri microarchitecture Steamroller, consist not only in small-scale and minor improvements, but on the contrary, they are visible to the naked eye. It is enough to look at the subsystem of the cache memory. In Steamroller, the second-level cache has halved in size and now only 1MB L2 is allocated to each dual-core module. But L1-cache of data, on the contrary, became twice more capacious. Its volume has increased to 32 K bytes per core, and its associativity has increased to eightfold, which should help reduce the share of misses.

As for the clock frequency, then, because of the orientation of the desktop Carrizo to the initial level, it is lower than the majority of Athlon X4 with the Kaveri design. The nominal Athlon X4 845 frequency is 3.5 GHz, but thanks to the Turbo Core technology available in this processor, it can dynamically rise to 3.8 GHz.

It is worth paying attention to the indicator of heat dissipation. For the Athlon X4 845, it is installed at 65 watts, which makes this processor one of the most economical offers in AMD’s quad-core line without integrated graphics. Curiously, a year ago, during the announcement of mobile Carrizo, company representatives claimed that the release of processors with such a design and thermal packs exceeding 45-watt is impossible. However, according to the characteristics of the Athlon X4 845, we see that then AMD was clearly cunning.

Another remarkable improvement in the Athlon X4 845 compared to its predecessors is the appearance of support for AVX2 instructions. Intel has added this set of commands to its processors even in the Haswell generation, and now similar functionality is becoming available in AMD desktop products.

Summarizing the above, we present a table in which the characteristics of the Athlon X4 845 and other current CPU models are included in the same series.

Athlon X4 880K Athlon X4 8 70K Athlon X4 860K Athlon X4 8 45 Athlon X4 8 ] 40
The code name

Kaveri

Kaveri

Kaveri

Carrizo

Kaveri

The processor socket

Socket FM2 +

Socket FM2 +

Socket FM2 +

Socket FM2 +

Socket FM2 +

The number of nuclei / flows

4/4

4/4

4/4

4/4

4/4

The clock speed

4.0 GHz

3.9 GHz

3.7 GHz

3.5 GHz

3.1 GHz

The maximum frequency in the turbo mode

4.2 GHz

4.1 GHz

4.0 GHz

3.8 GHz

3.8 GHz

The unlocked multiplier

There are

There are

There are

None

No

L2-cache

2 × 2 MB

2 × 2 MB

2 × MB

2 × 1 Mbyte

2 × 2 MB

L3-cache

No

No

No

None

No

Support for DDR3

1866/2133

1600/1866

1600/1866

1866/2133

1600/1866

Extensions of the instruction set

SSE4.2, AVX, AES

SSE4.2, AVX, AES

SSE4.2, AVX, AES

SSE4.2, AVX2, AES

SSE4.2, AVX, AES

The built in graphics

No

No

No

None

No

The technology of production

28 nm

28 nm

28 nm

28 nm

28 nm

TDP

95 W

95 W

95 W

65 W

65 W

The official price

$ 99

$ 94

$ 79

$ 68

N / A

For the sake of completeness, it should be mentioned that Athlon X4 845 is based exactly on the same 28-nm semiconductor crystal Carrizo, as well as the mobile processors FX, A10 and A8 eight-thousand series. This crystal initially contains 3.1 billion transistors and has an area of ​​250 mm 2 . However, in Athlon X4 845, its significant part simply does not work – in this processor not only the graphics core is disabled, but also the components of the south bridge, which among other things are available in the mobile chip Carrizo.

 The semiconductor crystal Carrizo "height =" 498 "width =" 800 "/>


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The semiconductor crystal of Carrizo

As a result, in the desktop version of Carrizo, no more than half of the original crystal actually functions. In other words, with the launch of the Athlon X4 845, AMD was more likely to prioritize the opening of the channel for the sale of production culls, rather than the development of the Athlon X4 line.

The fundamental differences between Athlon X4 845 and all other Socket FM2 + processors lead to the fact that this novelty is compatible with the existing motherboard park only after the UEFI update. However, it is unlikely that this will be a serious problem. All the leading manufacturers have already released firmware versions with the necessary changes.

⇡ # Microarchitecture Excavator

So, the emergence of the Athlon X4 845 introduces a couple of new code names to the lexicon of desktop supporters: Excavator is the new, following the Steamroller microarchitecture of the Bulldozer family, and Carrizo is the design of hybrid processors assembled from Excavator cores and the GCN 1.2. It should be noted that Excavator is the final point of development of the microarchitecture of the Bulldozer family. Next to it, AMD’s new microarchitecture Zen should come to AMD processors, with the introduction of which the company connects ambitious plans on its return to the position of the leading player in the processor market. And when talking about the transition from Excavator to Zen, it’s necessary to remember one more codename: Bristol Ridge are promising “intermediate” processors for mobile and desktop systems that will transfer the Carrizo design to the Zen ecosystem and achieve its initial adoption by the industry even before the emergence of radically new APU and CPU.

All this means that the microarchitecture Excavator will not become a guest in the desktop segment. She has a fairly serious role. In fact, she will accompany us until early 2017. Athlon X4 845 is a kind of test ball, in which we have the opportunity to make an initial opinion about this microarchitecture even before the appearance of the new Socket AM4 platform and Bristol Ridge processors on the market.

We have already published quite detailed material on the Carrizo processors in general and the Excavator microarchitecture in particular. Here we simply mention the basic facts sufficient to understand what is so notable for the Athlon X4 845.

And start with the most important: Excavator is the same 28-nm processor microarchitecture, as the previous Steamroller, but redesigned to improve energy efficiency. Design Excavator was conducted with a view to getting processors into a 15-watt thermal package, and as a result, this microarchitecture really shows an impressive increase in performance in conditions of a rigid framework for heat generation. But this is primarily due to the higher clock speeds that the Excavator achieves with severely limited power consumption and heat generation.

The key to the conquest of such boundaries was the use in the design of the core of technology libraries with a high density of transistors, which are usually not used when developing traditional processors. This approach is more typical for the GPU, but in this case it was also useful when creating an energy-efficient processor design. The density of the transistors of the semiconductor crystal Excavator compared to the Steamroller increased by an average of 23 percent, and in the case of Carrizo this freed up an additional transistor budget for embedding a more powerful graphics core and components of the south bridge into the processor.

However, technological improvements alone do not stop there. AMD promises that at the same frequency Excavator can perform 4-15 percent more instructions compared to Steamroller due to improvements at a low level of microarchitecture. This advantage is achieved due to the increase in the size and change of the algorithms of the cache memory of the first level. In particular, the capacity of L1-cache data in Excavator has doubled – up to 32 K bytes per core. In addition, AMD says about reducing the latency of this cache, coupled with improving the efficiency of pre-fetching data.

Another reason for improving the IPC (the number of instructions executed per cycle) is a 1.5-fold increase in the branch address buffer size. This makes the prediction of transitions in the Excavator core statistically more correct. In the case of errors, the microarchitecture Excavator promises an accelerated reset of the pipeline of real numbers.

It only remains to add to the portrait of Excavator the appearance of support for AVX2-instructions – a set that includes vector 256-bit integer instructions and vector instructions for operations with three operands. However, while these instructions are not used in real programs very often, and do not forget that they are executed by the FPU, which in Bulldozer class architectures is only one for every two cores.

In other words, there are no special advantages for Excavator. And all the promised progress can easily be reduced to zero by a decrease in the L2-cache volume, the size of which is now not 2, but 1 Mbyte for each dual-core module. In other words, quad-core processors with Excavator microarchitecture have a total cache of only 2 MB, which for many modern applications may not be enough. And especially this drawback is especially for APU, in which the third level of caching is not provided at all.

⇡ # North Bridge and memory subsystem performance

It seems that the bulk of the changes in Excavator compared to the Steamroller are performed in the memory subsystem. This is in part true, but not all changes can be assessed with a plus sign. Yes, the L1-cache has become bigger and more efficient, but the second-level cache memory has seriously suffered – its total size in Athlon X4 845 has decreased to a modest 2 MB (similar cache volume is typical only for Intel Celeron processors), and the rest of Athlon X4 can boast 4-megabyte L2-cache.

Another blow to the performance of the memory subsystem was found through the north bridge built into the Carrizo processor crystal. Its frequency in the Athlon X4 845 is reduced to 1.1-1.3 GHz (the exact value depends on the load), while in the Kaveri family the north bridge operates at 1.8 GHz. Considering that the memory controller is part of the built-in north bridge, we can expect that the performance of Athlon X4 845 will be lower when working with DDR3 SDRAM than for processors with an earlier design.

It’s not difficult to check all this. For this we used the traditional tool – the Cache & Memory Benchmark utility from the AIDA64 package. The test was carried out for quad-core Athlon X4 860K (Steamroller) and Athlon X4 845 (Excavator) operating at the same fixed frequency of 3.5 GHz with the same DDR3-2133-memory with the delay scheme 9-11-11-31.

Результаты вполне ожидаемы и объяснимы. Скорость кеш-памяти у Carrizo, как и обещала AMD, стала выше, что отчасти компенсирует её меньший суммарный объём. Но вот с основным массивом оперативной памяти процессор с новой микроархитектурой Excavator работает заметно хуже. Особенно сильно это проявляется в выросшей почти на 20 процентов латентности – сниженная частота работы северного моста не могла не дать о себе знать. Очевидно, что за счёт этого разработчики AMD хотели сделать Carrizo экономичнее, но в данном случае такое стремление негативно повлияло на производительность.

Кстати, мобильные корни Carrizo видны и ещё в одной неприятной особенности встроенного в Athlon X4 845 северного моста. Расположенный в нём контроллер графической шины обладает лишь восемью линиями PCI Express 3.0. И это не только лишает пользователей десктопного Carrizo возможности построения мульти-GPU конфигураций, но и вносит дополнительные ограничения в производительность видеоподсистемы.

Конечно, пропускной способности шины PCI Express 3.0 x8 для современных графических карт в большинстве случаев вполне достаточно, но это не отменяет того факта, что в сборках на базе Athlon X4 845 графика в любом случае будет работать не в полную силу.

⇡#Особенности турборежима

При тестировании Athlon X4 845 мы заметили, что технология Turbo Core работает в нём не совсем так, как у его предшественников с дизайном Kaveri. Раньше турборежим у Socket FM2+-процессоров включался только в том случае, если вычислительная нагрузка ложилась не более чем на половину ядер, а встроенные в процессор датчики фиксировали благоприятный температурный фон. По этим причинам повышенную тактовую частоту у Kaveri можно было наблюдать лишь при малопоточной и достаточно лёгкой нагрузке. В ресурсоёмких же приложениях частота всегда сбрасывалась до номинального значения или даже ниже.

У Athlon X4 845 же всё стало совсем по-другому. В процессорах поколения Carrizo работа технологии Turbo Core привязана исключительно к показаниям встроенных в ядро датчиков температуры и потребляемой мощности и никак не зависит от того, какое количество ядер процессора реально работает, а какое находится в состоянии простоя. А если к этому прибавить тот факт, что для Athlon X4 845 установлен достаточно либеральный для чипа с мобильными корнями тепловой пакет, то становится совершенно очевидно, что переходить в турборежим он способен гораздо чаще. И действительно: несмотря на то, что номинальная частота Athlon X4 845 – 3,5 ГГц, в большинстве случаев этот процессор работает на 3,7-3,8 ГГц. Причём, активация турборежима нередко происходит даже при исполнении ресурсоёмких многопоточных программ.

В качестве иллюстрации покажем, например, как изменяется реальная частота во время прохождения стресс-теста в LinX 0.6.5.

Даже в течение создающего очень серьёзную нагрузку теста стабильности частота вычислительных ядер тяготеет к величине 3,8 ГГц. Иными словами, переходить в режим с повышенной частотой Athlon X4 845 умудряется при весьма тяжёлой нагрузке. Процессоры поколения Kaveri на такое были совершенно неспособны. Получается, что по средней реальной частоте работы Athlon X4 845 сопоставим с Athlon X4 860K: Carrizo почти всегда работает с активированным турборежимом, а Kaveri наоборот – чаще функционирует в своём номинальном режиме. Впрочем, справедливости ради стоит отметить, что провалы частоты ниже штатного значения – в данном случае до 3,1 ГГц – никуда не делись и у Athlon X4 845. Но теперь их можно наблюдать лишь эпизодически.

Столь охотное включение процессором Carrizo турборежима подкрепляется и ещё одним наблюдением: нагрев Athlon X4 845 во время работы очень скромен. В тестировании мы по традиции пользовались воздушным кулером Noctua NH-U14S, и максимальная температура CPU, которая была зафиксирована во время прогонов теста LinX, достигала лишь 39 градусов (согласно показаниям термодатчика в процессорном гнезде). Так что причины агрессивности технологии Turbo Core у Athlon X4 845 не вызывают никаких вопросов.

⇡#Разгон

Процессор Athlon X4 845 относится к числу бюджетных и потому не входит в оверклокерскую серию, что однозначно следует из его модельного номера, в конце которого нет литеры К. Это значит, что его множитель заблокирован, и 35x – это максимальный коэффициент умножения, который можно выставить в BIOS материнской платы для данного CPU. Тем не менее разогнать Athlon X4 845 всё-таки можно: современные Socket FM2+-материнские платы позволяют покорять повышенные частоты другим способом – через увеличение частоты BCLK.

Впрочем, даже с учётом имеющегося обходного пути особых достижений в плане разгона от Athlon X4 845 ожидать не стоит. Не забывайте, этот процессор основан на дизайне Carrizo, который имеет мобильные корни и нацелен на энергоэффективность, а вовсе не на работу на высоких тактовых частотах. К тому же разгон через увеличение частоты основного тактового генератора в Socket FM2+-системах не всегда проходит безболезненно. Например, при таком подходе к оверклокингу часто возникают сбои в работе встроенного в чипсет SATA-контроллера, лечить которые с переменным успехом приходится его переводом из AHCI в IDE-режим и дополнительным увеличением напряжений VDDA и APU1.2V.

Но и даже после всех подобных ухищрений разгон десктопного Carrizo не даёт особых поводов для радости. Например, наш экземпляр Athlon X4 845 продемонстрировал устойчивую работоспособность лишь на частоте 4,2 ГГц, которая была достигнута увеличением BCLK до 120 МГц.

Для обеспечения стабильности в таком состоянии напряжение на процессоре пришлось поднять до 1,6 В, но в данном случае эта величина не кажется чрезмерной – штатное напряжение процессоров Athlon X4 845 находится в диапазоне 1,46-1,49 В. Не давал никаких поводов для беспокойства и температурный режим. Нагрев разогнанного процессора во время тестирования стабильности в LinX, по данным термодиода под процессорным гнездом, не превышал 44 градусов. Кстати, пользоваться именно расположенным на материнской плате термодатчиком, а не измерительными средствами самого CPU заставляет традиционная для продукции AMD странная калибровка, из-за которой показатели встроенных в Carrizo термодатчиков совершенно неправдоподобны.

Подытоживая всё сказанное в данном разделе, остаётся признать, что Athlon X4 845 – очень плохой кандидат для эксплуатации на повышенных частотах. Разгонять его сложно из-за нестабильности материнских плат при ускорении базового тактового генератора, а частотный потенциал самого этого чипа значительно ниже, чем у его собратьев из семейства Kaveri. И это обусловлено не неудачностью конкретного экземпляра CPU, а глобальными причинами – оптимизацией для мобильного применения и в первую очередь высокоплотной компоновкой транзисторов в полупроводниковом кристалле Carrizo.

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