SiFive offers potential Neoverse N2 rival – the P870-D RISC-V core for datacenters

Chip upstart takes aim at Arm with design that can scale up to 256 cores

SiFive has announced the launch of its latest core for datacenters, the P870-D, and claims it has a leg up on Arm's Neoverse N2 in density for AI.

The P870-D is a datacenter-focused variant of the RISC-V-powered P870 core, which debuted about a year ago. The main upgrades for the P870-D include its rest capability, error detection, 57 bits of virtual addressing for more memory, and the ability to scale up to 256 cores in a single SoC, which can optionally be monolithic or chiplet-based. 

These datacenter-focused improvements are why the new core has that "D" at the end, though SiFive senior director Ian Ferguson told The Register that the company agonized for a while over whether to add that letter or make up a fresh model name for its new core.

Ferguson says the P870-D doesn't try for top-end performance but instead balances speed with efficiency. The core is apparently on par with Arm's Neoverse N2 – which features in Microsoft's Azure Cobalt 100 – in terms of performance, but is about 25 percent smaller.

When we asked Ferguson about efficiency though, he said it was hard to quantify since it depends on the process node; SiFive has modeled out the P870-D characteristics on TSMC's 3nm, but many customers are taping out cores on the older 7nm node. If the picture is unclear, we can probably assume the P870-D at least isn't always the clear favorite to win in a contest of efficiency against the N2.

CPUs based on the P870-D are expected to be used for running storage servers, video streaming, traditional datacenter work, and parallel workloads in general, according to Ferguson. Although SiFive's press statement mentions AI rather prominently, Ferguson says the P870-D won't be ideal to run AI workloads directly, since it only has some vector instructions compared to Intel's Xeon CPUs.

Instead, the P870-D is more ideal to pair with AI-focused processors, like Nvidia's GPUs and perhaps Google's Tensor Processors.

The P870-D core won't immediately propel SiFive into the same league as Arm when it comes to market share and revenue, Ferguson says. Those things will take time, and there won't be a "massive impact" on the firm's finances in the short term. In the long term, however, the RISC-V company bets it'll be successful.

SiFive is sampling the P870-D to customers in the US, EU, and China currently, and expects the first tapeouts to happen in December. ®