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posted by Fnord666 on Thursday October 31 2019, @02:06AM   Printer-friendly
from the processing-in-a-disorderly-manner dept.

SiFive Announces First RISC-V OoO CPU Core: The U8-Series Processor IP

In the last few year's we've seen an increasing amount of talk about RISC-V and it becoming real competitor to the Arm in the embedded market. Indeed, we've seen a lot of vendors make the switch from licensing Arm's architecture and IP designs to the open-source RISC-V architecture and either licensed or custom-made IP based on the ISA. While many vendors do choose to design their own microarchitectures to replace Arm-based microcontroller designs in their products, things get a little bit more complicated once you scale up in performance. It's here where SiFive comes into play as a RISC-V IP vendor offering more complex designs for companies to license – essentially a similar business model to Arm's – just that it's based on the new open ISA.

Today's announcement marks a milestone in SiFive's IP offering as the company is revealing its first ever out-of-order CPU microarchitecture, promising a significant performance jump over existing RISC-V cores, and offering competitive PPA metrics compared to Arm's products. [...] SiFive's design goals for the U8-Series are quite straightforward: Compared to an Arm Cortex-A72, the U8-Series aims to be comparable in performance, while offering 1.5x better power efficiency at the same time as using half the area. The A72 is quite an old comparison point by now, however SiFive's PPA targets are comparatively quite high, meaning the U8 should be quite competitive to Arm's latest generation cores.

Performance gains over previous designs are substantial:

The performance increases compared to previous generation SiFive cores are extremely impressive: Against a U54 at ISO-process, the new U84 features a 5.3x performance increase in SPECint2006. When taking into account the process node improvements that allow the U84 to clock higher, the generational increases that we'd be seeing in products will be more akin to a factor of 7.2x.

In terms of PPA, compared to a U7-series CPU, IPC increases come in at 2.3x resulting in 3.1x higher performance (ISO-process). A lot of the performance increases of the U8-series come thanks to the increased frequencies capabilities which are 1.4x higher this generation, with the core scaling up to 2.6GHz on 7nm.

On the same 7nm process, the U84 lands in at 0.28mm² per core and a cluster comprising four cores and a 2MB L2 cache measure in at 2.63mm². For comparison, an Arm Cortex-A55 as measured on the Kirin 980, also on 7nm, a core with its 128KB private L2 cache comes in at 0.36mm². Given that SiFive promises of similar performance to a Cortex-A72, which in turn would be more than double the performance of an A55, it looks like SiFive's U84 core would be extremely competitive in terms of its PPA.

Related: Qualcomm Invests in RISC-V Startup SiFive


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  • (Score: 2) by DannyB on Thursday October 31 2019, @08:26PM

    by DannyB (5839) Subscriber Badge on Thursday October 31 2019, @08:26PM (#914315) Journal

    I agree.

    It's the same old argument and history playing out but in hardware.

    fanboy: "But Windows isn't that expensive, in fact it's include on the PC and subsidized by the included malware. It's great!"

    But I believed even in 2000 that open source would win. Trying to stop it is like trying to stop the incoming tide on the beach by using your hands. Or trying to prevent the sun from shining by holding your hands up in the sky to cover the sun. The force of open grows and in time becomes overwhelming. But proprietary sure did beat it for marketing, short term penetration, and a seeming gloss of skin deep quality. But here we are today and Linux and other open source powers everything. Microsoft is trying to embrace it all as fast as they can.

    It will be the same with hardware. Some closed designs. But I think open is what will ultimately win. I would simply ask what was it that motivated the entire RISC-V design and effort in the first place? Those motives are still in play. And more and more users will realize how those open motives benefit them in a tangible way, while the addictive sweetness of proprietary is like a drug dealer's first hit for free.

    --
    People today are educated enough to repeat what they are taught but not to question what they are taught.
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