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Arm’s Neoverse V2
- metadat 3y agoAre there simulators that chip developers use to get an idea of what performance will be for certain workloads prior to creating an engineering sample? Or how does this work?
- frogblast 3y agoIdeally they know exactly how it will perform: Every part of the chip, including the caches, memory controller, and DRAM is implemented in a cycle accurate simulator. There are often multiple versions of that simulator, one written in C/C++ that matches the overall structure of the eventual hardware, and then simulations of the actual RTL (hardware source code, networks of gates). The C-model and RTL model outputs are often also compared with each other as a correctness validation step, as they should ideally never diverge. (ie, implement twice, by two teams, and cross-check the results). Those simulations are terrifically slow for larger chips, so there is a surprisingly small number of workloads that can be run through them in reasonable time. So there tend to be even more simulator implementations that sacrifice perfect performance emulation for 'good enough' performance correlation (when surprises can happen). Being able to come up with a non-exact simulator that perf-correlates with real hardware is an art in itself.
- sol91949 3y agoAre the C simulators hand crafted each time by the chip designer? It seems like the kind of thing that needs custom built but I’m wondering if there is a common toolset used, or platform?
- KptMarchewa 3y agoThe "exact" part is not exactly true for modern computer processors, where thermal and power constraints are a problem, right?
- wmf 3y agoThe performance team usually thinks in terms of cycles. At runtime the frequency varies depending on various factors as you said, but this is mostly ignored.
- universal_sinc 3y agoAbsolutely! Chip designers have a several tools to do this. First, they create detailed software models (usually in C++) of their chips to estimate performance as closely as they can before laying out a single transitory. These models can run code just like a real hardware device, albeit slowly. Once the chip is designed, verilog simulators are programs used to generate the exact logical output of a circuit, which can be used to measure performance on a workload. However, this method is even slower than the first! For larger workloads and higher speed, they use extraordinarily expensive FPGA-based platforms called Emulators. This allows circuits to be run at speeds in the MHz range before ever being sent to a fab. Booting an OS, running a complex multicore workload with shared memory, they can measure almost any workload. But this method is not available until late in the design phase and the boxes themselves are prohibitively expensive from being deployed very widely. The software models are the most useful for estimating performance, as long as they are written early and well :)
- vintagedave 3y ago> they create detailed software models (usually in C++) of their chips to estimate performance as closely as they can How does this work? Do they model at the transistor level, or at the level of logical functions, or..? I'm particularly curious how this can estimate performance if it's anything higher-level than a direct transistor-for-transistor, layout-aware, emulation. I'd be really interested in learning more if there's anything you could share, please. I can find info about chip design software and languages like Verilog (as you mention) but not this sort of modeling.
- nudgeee 3y agoWhen I was in chip design about 15 years ago, we did transaction level modeling (TLM) using SystemC. Not sure if it’s still a thing these days. https://en.m.wikipedia.org/wiki/Transaction-level_modeling https://en.m.wikipedia.org/wiki/Transaction-level_modeling
- amelius 3y agoBasically you model all the elements of a chip (queues, memory, alus, etc), and how much time they take. You use a virtual clock so your simulation model can run at a different pace.
- synergy20 3y agosystemc is a c++ derivative often used to model chip designs. Before chip tapeout most of the chip design has been fully simulated and emulated many many times, be it functional wise, or cycle by cycle(e.g. cycle accurate simulation).
- andromeduck 3y agoThat just gave me PTSD. System C is terrible.
- synergy20 3y agoit's c++17 for me, I don't feel much difference at all between c++ and systemc.
- epilys 3y agoArm has "Fast Models": https://developer.arm.com/Tools%20and%20Software/Fast%20Models https://developer.arm.com/Tools%20and%20Software/Fast%20Mode...
- StillBored 3y agoThose aren't for quantifying performance, they are for developing the firmware/OS/software stack to run on the platform. In other words, they are a slightly more accurate version of something like QEMU, although I guess I should point out they can generate traces that can be fed into tools to model HW perf, ex gem5.
- epilys 3y agoSecond sentence in link: "They allow full control over the simulation, including profiling, debug and trace."
- aidenn0 3y agoI'm still not sure which ARM cores are the "most fair" to compare to laptop/desktop x86oids and Apple M series; The N2, the A710, something else?
- re-thc 3y agoThe irony, where Apple M series is an ARM core...
- aidenn0 3y agoARM as in "Designed by ARM Ltd." not ARM as in "Uses the aarch64 ISA"
- MobiusHorizons 3y agoWhile Apple M runs Arm instructions, it is not any of the cores designed by Arm like the cortex A7 series or the X series. While those chips come in packages from other manufacturers (ie Mediatek, Qualcom, or even Google's tensor) the actual core design is from ARM, but is tweaked (usually things like cache sizes can be adjusted) and integrated with other supporting hardware by the manufacturer. Apple's cores are actually completely custom, with no input from ARM the company.
- menaerus 3y ago> While Apple M runs Arm instructions, it is not any of the cores designed by Arm like the cortex A7 series or the X series How can we be sure about this since Apple does not disclose any details about their chips? > Apple's cores are actually completely custom, with no input from ARM the company. Apple is one of the founders of ARM, with other two being Acorn Computers and VLSI Technology.
- zyedidia 3y agoI think the Cortex-X series cores are the ones starting to make their way into laptops and the like (Cortex-X4 is the latest). These are Arm's "flagship" cores.
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- jonstewart 3y agoWhither SVE? Will trying to use 256 bit vectors still result in the sad trombone condition register getting set?
- brucethemoose2 3y agoIts 4x128 bit units now. TBH this makes sense, as pretty much all the ARM code in the wild will be using NEON.
- Symmetry 3y agoIf you could get your hands on a Fujitsu A64FX you could get some really wide SVE vectors but those aren't really supposed to be for consumers.
- ksec 3y agoSo I guess that is reason why AWS went with V1 and 5nm. V2 isn't quite attractive in terms of Die Space, Node and Power usage. Graviton could trade for more V1 Core instead of top single core V2 performance. I am hoping post ARM IPO we will have Cortex X5 and N3, V3 announcement. Also waiting if Apple A17 will gain any more double digit percentage IPC improvement. Personally I dont think that will happen.
- akmittal 3y agoI didn't know NVIDIA makes server ARM chips. Their tegra processor was promising, specially the GPU part. I hope they bring it back.
- shaklee3 3y agoTegra hasn't gone away. A new version just came out called the Orin.
- akmittal 3y agoIt does not seem like what tegra used to be, looks like for automotive only https://wikimovel.com/index.php/Nvidia_Tegra_Orin https://wikimovel.com/index.php/Nvidia_Tegra_Orin
- saagarjha 3y agoIt’s more than capable for general-purpose use; you don’t have to use the lockstep if you don’t want it.
- rayiner 3y agoSounds like the V2 is about as wide in issue width at Apple’s M1/2 (8 MOPs) but not nearly has deep (~300 versus over 600). Can ARM actually keep such a wide architecture busy?
- andy_ppp 3y agoI’d love to see a performance per dollar article on these machines. Is there anything out there? My guess is they’ll be efficient in terms of cost to buy and cost to run compared to the competition and I wonder if it’s worth trying out?
- drcongo 3y agoI've been running a few sites on Hetzner Cloud's ARM machines and at a guess I'd say performance is extremely close on the 4 core ARM to the 4 core Intel / AMD, and it's a quarter of the cost. I've not seen any issues with them at all either. The bonus is that, being far more energy efficient, they're theoretically greener too. I wonder what the carbon savings would be if every server switched to ARM?
- bArray 3y agoThe CMN-700 12x12 mesh seems interesting to me, I think this very much needs to be explored more. I hope somebody builds one!