Hi all, I've been thinking recently about computing, and how an ideal community would move forward with MPIR development. I realise we don't actually have all that much of a community left, but perhaps my comments will inspire a new generation of developers to pitch in, as I myself am totally engaged with other projects nowadays and don't have time to commit to MPIR.
Currently I see no reason to duplicate work being done in the official GMP project. They are doing a good job of supporting modern CPU microarchitectures. I believe MPIR development effort should focus elsewhere. But let me explain why that is. There's a perception in our community (at least amongst older researchers) that once clock speeds leveled off in about 2004/5 that Moore's law was at an end for single core performance. (GMP and MPIR are currently single core libraries.) But that perception is not correct. In fact, single core performance of CPU's has increased unabated, with a predicted leveling off only in the next year or so, with a few minor improvements yet to come due to shrinking of dies. Whilst clock speeds have not gone up, pipelines have gotten deeper, numerous new features have been added, including various revisions of SSE and then AVX, more integer ports, specialised instructions for multiprecision arithmetic (yes the kind GMP/MPIR specialise in), performance management through temperature profiles, hyperthreading (though this is usually useless for superoptimised code; it's great for code coming from a C compiler, depending on the application) and more recently real-time AI adjustment of silicon usage to optimise performance. All of this development means that nothing prior to Intel's Core architecture and nothing prior to AMD's K10 architecture is now relevant, even for single core performance. But even these won't be relevant much longer. There's a feeling that this past year, Core 2 has finally become totally obsolete. Looking to the future, bigger changes are coming. Because yields go down as die sizes go up, it is inevitable that large monolithic CPU cores will give way to a far greater number of smaller dies, especially as we move from the current 14nm technology to an eventual 5nm, where things will surely start to get really hard (Intel is already reportedly having major problems with yield at 10nm). Then there's the performance decreases we have seen due to Spectre and Meltdown. A lot of the superoptimisation MPIR does is surely worthless in light of this. I see more and more of this sort of thing happening in the future. Like it or not, the era of single core performance increases is almost at an end. MPIR is also about 3-5 years behind anyway; the latest Intel microarchitecture we optimise for is Skylake, which was 2015 and the latest AMD microarchitecture we had a good look at was Piledriver, from 2012, not that AMD has been terribly relevant in the period 2012-2016. Admittedly server architectures are usually a few generations behind desktop architectures. But the face of CPU and computing technology development is all changing fast. Abstractly, modern computer processors consist (or will consist) of three components, a CPU, GPU and TPU (tensor processing unit). The CPU as we know it is becoming less relevant every day (it will still continue to exist, but will change radically; for example I/O, memory controllers and cache will be separated from an increasing number of small dies for arithmetic pipelines). Modern Ryzen/Threadripper/EPYC CPU's from AMD already basically use a kind of TPU to control the temperature profile of the CPU (switching silicon on and off and scheduling which silicon does what). Result: 10-30% performance improvement by adapting to the values coming from bazillions of sensors, based on what code is currently running. Modern EPYC server racks have 640 CPU cores, but this is a tiny fraction of their compute power. By far, the greatest part of their compute power is in their GPU's. If I have my calculations correct, in excess of 320,000 GPU cores (actually there are three different kinds of cores in the GPU's), all in a 1U rack. These are targeted at Data Centres, AI research and Scientific computing, but why not also computer algebra system users? You can use a GPU for Groebner basis computations or for linear algebra, right? Why not other things too? Still worried about memory bandwidth? How does 11 Gbps sound? Then there are tensor cores. Nvidia's Volta architecture has 640 Tensor cores, for 100 teraflops per device. Google's second generation TPU's (what Google use in their data centres for photo processing and Google ranking: 100 million photos processed per day per device) are 15-30 times faster than Nvidia's GPU's for many tasks (23 petaflops per rack). And Nvidia are already ahead of AMD (who make Ryzen, Threadripper and EPYC). It's very clear that the future of MPIR is in multicore/GPU/TPU code. This means a fundamental change in approach, and a lot of work. If I were a young person looking to get involved in this, I would purge MPIR of support for anything older than Core 2 Duo or AMD K10 and use fallback C code on everything that is not AMD or Intel. I'd wouldn't worry about support for Pentium and Atom. I'd support only I3/I5/I7/I9 and Xeon. I wouldn't waste my time catching up on the AMD side of things. I'd start with Zen support only (Ryzen, Threadripper, EPYC). I'd radically simplify the build system, ditching the legacy autotools, which is approximately useless, and adopt something more modern. I'd dump code from MPIR that isn't faster than GMP (the FFT and divide and conquer division code should still be used from MPIR, I believe) and try to get the two libraries as close together as possible so that taking code from GMP to MPIR is easy. Then I would make the big change: switch development effort to supporting GPUs and eventually TPUs. There's lots of interesting challenges here, both theoretical and practical. The future is here today, and younger people who want to get stuck in shouldn't wait for us old dinosaurs who aren't even up with the latest tech. I believe it's time for a new generation to gradually start taking over MPIR and showing us old dinosaurs the way forward. I'm looking forward to seeing what the next generation can do! Bill. -- You received this message because you are subscribed to the Google Groups "mpir-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to mpir-devel+unsubscr...@googlegroups.com. To post to this group, send email to mpir-devel@googlegroups.com. Visit this group at https://groups.google.com/group/mpir-devel. For more options, visit https://groups.google.com/d/optout.
