Because, without neglecting the micro-architecture, we all know how critical the silicon process is for high-end performance.
The point is that RISC-V is not limited to lower performance by the ISA.
But for SiFive's last silicon, the HiFive Premier P550, they claimed a specint2006 of 8.65/GHz. That should put the silicon only about 20% slower than an intel i5-6400. But if you look at geekbench scores it's about an order of magnitude slower.
Correct me if I'm wrong, but Tenstorrent has yet to ship any of their own cores? They do make very similar claims to SiFive.
Personally I'm very skeptical that these cores will be anywhere near Zen 3. I recon their performance claims are based on best-case CPU simulation, rather than a real measurement. I'd expect Raspberry Pi 4 levels of performance, a bit over double SiFive's current state of the art. An impressive improvement, but nowhere near Zen 3.
When I had brief access to a very early P870 devboard running at 2GHz it scored 2% worse than an 2.86GHz Cortex-X1 in the 7-zip benchmark compression (it was a 40% worse in decompression, but that has NEON optimized Arm assembly path and non for RISC-V). Because this was very early hardware still in bringup I expect them to get closer to the announced 2.7GHz.
But yeah, the RISC-V geekbench scores of publically available RISC-V processors are suprizingly low and idk why. Part of it is the lack of RVV support is certain workloads, but that doesn't explain the entire gap. When I looked at ST scalar performance my self it looked more comparible to similarly sized Arm CPUs.
I think I'll have to order a Pi5 (Cortex-A76) and investigate where it performes different to the SpacemiT K3 (SpacemiT X100).
On paper they should be very similar, both 2.4GHz, 4-wide decode, 3xALU, 1xBranch, (although the A76 has those on 4 execution units, while the X100 has 3 with one sharing ALU and Branch support), 2x load/store, 2xFP. The biggest obvious difference (appart from ISA), may be the cache setup after L1, with the K3 having a 4Mib L2 shared between 8 cores (no L3) and the Pi5 having a 512KiB L2 and a 2MB L3 shared between 8 cores.
Well, there is some speculation regarding these chips so no sense arguing too much about it.
That said, the SpacemiT K3 is already faster than a Pi 4 and even substantially faster than a Pi 5 for multi-core and vector stuff. And that is before counting the other 8 “AI cores” it has.
These chips will be quite a bit faster than a K3, so certainly much faster than a Pi 4.
> and even substantially faster than a Pi 5 for multi-core and vector stuff
I'll push back a little on this. It can be faster under certain workloads, but is not universally. It's behind in geekbench https://browser.geekbench.com/v7/cpu/compare/146501?baseline..., and in compilation workloads: https://www.phoronix.com/review/spacemit-k3-pico-itx/3