SiFive’s brand-new P550 is one of the world’s fastest RISC-V CPUs

Enlarge / SiFive’s “Important” household is stripped right down to the minimal configurations and efficiency vital for normal microcontroller responsibility. “Intelligence” provides AI/ML acceleration, and the brand new “Efficiency” household gives simply what it says on the tin.

As we speak, RISC-V CPU design firm SiFive launched a brand new processor household with two core designs: P270 (a Linux-capable CPU with full assist for RISC-V’s vector extension 1.0 launch candidate) and P550 (the highest-performing RISC-V CPU up to now).

A fast RISC-V overview

For these not instantly aware of RISC-V, it’s a comparatively new CPU structure which takes benefit of Lowered Instruction Set Pc (RISC) ideas. RISC-V is an open normal particularly designed to be forward-looking and evade as a lot legacy cruft as potential. One instance of this design is RISC-V’s dynamic width vector instruction set, which permits builders to execute vector directions on information of arbitrary measurement with most effectivity.

In conventional processor designs, a vector instruction has a hard and fast width tied to the {hardware} register measurement of the processor—for instance, SSE and SSE2 enable use of a Pentium III’s 128-bit registers, whereas making full use of an i7-4770’s 256-bit registers requires a totally separate instruction set (AVX2) for a similar mathematical operations. Shifting as much as an i7-1065G7’s 512-bit registers requires one more instruction set, AVX-512—once more, for a similar underlying mathematical operations.

In sharp distinction, RISC-V vector math permits a single set of CPU directions to carry out the identical set of mathematical operations as effectively as potential, utilizing no matter measurement registers the present CPU design has out there. This implies a developer can merely write a single routine that may course of vector operations as effectively as potential on a cellphone with 64-bit registers or on a supercomputer with 1,024-bit registers.

Along with forward-looking options constructed into the RISC-V spec, the structure is designed to supply flexibility that its designers didn’t or couldn’t consider forward of time. Generic RISC-V designs function reserved opcodes, which designers of particular RISC-V CPUs might then take over to supply further, arbitrary performance.

The flexibility to “take over” reserved opcodes permits for drastically streamlined ASIC design, since each specialised directions and normal controller performance will be supplied on a single die—and with out CPU architects needing to reinvent any wheels to supply the generic controller performance.

For the second, RISC-V just isn’t a severe competitor to both Arm or x86 within the general-purpose processor house, but it surely’s closely used within the microcontroller house, due partially to its extensibility and cheap licensing. We do broadly anticipate RISC-V to grow to be a 3rd main participant on the subject of general-purpose CPUs—the kind that present the “major mind” for telephones, tablets, and conventional computer systems—however that’s nonetheless some years away.

What’s new within the SiFive Efficiency household?

The 2 new designs introduced in the present day are P270 and P550. P270 is SiFive’s first CPU to totally assist the elective RISC-V vector extension 1.0 launch candidate, and P550 is SiFive’s highest-performing RISC-V processor up to now—additionally making it, so far as we all know, the highest-performing RISC-V processor out there.

P270 and “V” 1.0-rc1

SiFive's Recode automatically translates legacy SIMD source to SiFive vector assembly—in this case, beginning with source code written for Arm's Neon instruction set.
Enlarge / SiFive’s Recode robotically interprets legacy SIMD supply to SiFive vector meeting—on this case, starting with supply code written for Arm’s Neon instruction set.

As you’d anticipate from the “launch candidate” rider, RISC-V’s “V” elective instruction set just isn’t but a frozen normal. When the V spec reaches 1.0—with out the “launch candidate” rider—it is going to be thought-about steady sufficient to freeze the function set. This can enable builders to start work on long-term initiatives utilizing it for toolchains, useful simulators, and so forth, with some extent of certainty that the code the builders have written will “simply work” on future CPU designs.

It is price noting that even as soon as the discharge candidate tag is eliminated, the 1.0 model of the V directions will nonetheless solely be thought-about prepared for public ratification. The primary true manufacturing model of V shall be 2.0, a model quantity awarded after public ratification is taken into account full, with no main performance adjustments vital.

SiFive additionally gives a translation utility referred to as Recode, which robotically converts legacy SIMD code to V-spec vector meeting.

P550 excessive efficiency

This somewhat confusing trio of bar graphs shows a single P550 core significantly outperforming an equivalent Cortex A75 core (top two graphs) while blowing it out of the water in performance per on-die square millimeter (bottom graph).
Enlarge / This considerably complicated trio of bar graphs exhibits a single P550 core considerably outperforming an equal Cortex A75 core (high two graphs) whereas blowing it out of the water in efficiency per on-die sq. millimeter (backside graph).

Each P270 and P550 are Linux-capable designs, however the P270 is proscribed to a dual-issue, in-order pipeline with solely eight levels. Whereas the P270’s full V extension assist ought to make it a formidable processor for closely vector-math-dependent purposes, the P550 ought to show way more highly effective for purposes nearer to these presently dealt with by general-purpose CPUs.

SiFive’s new Efficiency P550 core includes a 13-stage, triple-issue, out-of-order pipeline. SiFive claims {that a} four-core P550-based CPU takes up roughly the identical on-die space as a single Arm Cortex-A75, with a big efficiency benefit over that competing Arm design. SiFive says the P550 delivers 8.65 SPECInt 2006 per GHz, primarily based on inner engineering take a look at outcomes—a laudable outcome when compared to Cortex-A75 (and never too far behind an i9-10900K’s 11.08/GHz). Nevertheless it’s properly behind an Apple A14’s 21.1/GHz.

Intel adopts P550 to be used in its Horse Creek platform

Before everything, we have to make one factor clear—we’re nearly definitely not speaking about Intel ditching the x86_64 structure for RISC-V! Fashionable x86_64 CPUs from Intel and AMD embrace administration and supervisory cores, which aren’t instantly accessible to finish customers. These are sometimes Arm CPU cores; for instance, AMD’s first APUs used Cortex-A5 for his or her platform safety processor.

The joint announcement from Intel and SiFive is unclear on simply what Horse Creek shall be. Intel usually reserves the “Creek” names for socketed platforms moderately than all-in-one system on chip (SoC) boards. This implies that, in all chance, the P550 shall be restricted to supervisory or administration duties inside x86_64 Horse Creek CPUs moderately than instantly processing directions from software program working on that platform.

Anandtech’s Ian Cuttress points out that constructing the P550 instantly into Horse Creek—which shall be constructed on Intel’s latest 7nm course of node—may present Intel with less complicated testing and extra fast improvement of the brand new 7nm course of itself.

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