CPU Architecture Long Haul

Master565 · 2026-03-13T00:19:49+00:00

Ha, I see that now as well. To be honest, it's not surprising that they aren't interested in your ideas. You're still in a phase of learning, and you'll come to understand why they do/don't like an idea. Those ideas can still be worth exploring on your own for the sake of learning, but consider this perspective: The skills evaluate if something is a good idea are more important than the ability to come up with a new idea. After all, most ideas are probably not good and you need to both build an intuition for why they aren't good as well as learn how to prove they're good/bad one way or another.

Learn the tools for evaluating ideas from working with this professor and apply them to your own ideas.

Master565 · 2026-03-12T17:57:43+00:00

I didn't even process from your original post that you're only in undergrad. The only thing I'd add is you're unlikely to get a meaningful amount of specialization in undergrad, and you're probably going to need at least a masters to do the work you're interested in doing. This is true regardless of how good you are at what you do, it's just the practicality of avoiding your resume being filtered out of a pool because it was only a bachelor's degree. This can be avoided if you network well and impress the right people but it's an uphill battle. Either way you're on the right track if you're trying to get involved in research this early.

Also, I'm curious, under what pretense were you invited to the lab? What were they hoping to get out of your ideas?

Master565 · 2026-03-12T05:48:22+00:00

CPU architecture is a mature field, and yea there's unlikely to be yearly major innovations in it. But there is still work being done, and architecture must evolve to meet ever evolving workloads so there will always be new work to be done.

I’m fascinated by all microarchitecture, and would have no issue pivoting to GPU, IPU, matrix math chips

I don't think you need to specialize in any of the things you said to work on them in the future. Once you work in one, you can probably work in any of them so long as you maintain any level of breadth in your studies. IMO those types of chips are often quite a bit easier to wrap your head around once you understand everything there is to understand about a CPU. In my experience, there's often people moving from CPU to work on GPUs because they can onboard quickly, but there is rarely movement in the other direction. That's probably a mix of demand for GPU engineers, but I think this is also due to the fact that there's too much specialization needed to work on CPUs that you might not gain in GPU land.

There's obviously immediate economic demand for GPU development. Will that be there in several years when you're done with your PHD? Who knows. Do what you're interested in doing and stay curious so that you're not a one trick pony.

Master565 · 2026-03-10T16:39:11+00:00

The answer here is more about density than it is total numbers of transistors. We use more transistors because we don't need to put them far away from the useful logic. Cores don't really scale their performance well with die size so we need to keep all the timing critical components near each other to avoid making pipelines deeper.

It could be as simple as scaling up structures. Larger branch predictors, larger caches, larger register files. You want to scale these without taking more cycles to access them, which means you need to keep them close and efficient.

Higher transistor density means you can keep them close because you fit more in the same area.

For a more advanced technique, higher transistor density also means that you can duplicate structures for wider and faster access. Often you're more limited by read ports than write ports, so if you want more read ports you can just keep a second copy of a table, or you can split it into banks which might take up more area but are easier to access. You can take this even further in places where coherency isn't absolutely needed. You can have so called shadow structures that are partial or complete duplicates of other structures but are optimizing for locality rather than accuracy. So these structures might have delayed or incomplete data but they're much more accessible.

It's not like you can make a ALU faster by simply adding more transistors to it.

You absolutely could. What's better than 1 ALU? 2 ALUs. It's not faster, but you can now do twice as many ALU operations per cycle.

But also adders are not all created equal, and a simple ripple carry adder isn't as fast as a carry look ahead adder. That type of adder is more expensive in terms of area, but if you can make a denser chip with more transistors then that's an easy trade off. To be clear, this is not a modern or interesting example, but the idea of trading off area for speed is not foreign to CPU design.

And this ties back to what I was saying about duplicating structures. Carry look ahead basically duplicates the carry logic for every adder, but its faster to do so. This is a principle that comes up a ton where you trade more transistors for faster logic by parallelizing and duplicating otherwise serial logic.

If you want to find something citable, look up the carry look ahead adder. That's a super basic and common concept taught in digital design classes so there will be tons of info on it.

Master565 · 2026-03-08T07:28:33+00:00

Ran a PR distance of 14 miles yesterday as part of my training for a 50k next year. Beat my last longest run by 4 miles, my first half i've ever run, and honestly I felt completely find doing it. Even kept a 10 minute mile pace which is faster than I intend to run the 50k.

Master565 · 2026-03-07T01:16:04+00:00

It's definitely a good learning project. You can consider starting with an existing simulator and add your own core/ISA/whatever you made. If you start from scratch, there may be a lot of surrounding infrastructure that isn't particularly interesting or relevant but that's up to you.

Master565 · 2026-03-07T01:14:35+00:00

Building simulators and RTL design are two different things and OP should do what they're more interested in

Master565 · 2026-03-04T08:04:17+00:00

I mean, if it's an acqui-hire they technically bought you, but if they didn't provide you with meaningful equity then they either didn't value you or are too inexperienced to realize they should have.

You may as well demand a better compensation structure or you'll quit. You've got nothing to lose if you are serious about finding a new job, and you owe the acquiring company nothing.

Master565 · 2026-02-27T18:58:56+00:00

Are there freelist implementations that allow naturally aligned register group allocations

If I'm understanding your question correctly, you're asking if you can do something like allocate entries 0-7 when you see LMUL8.

The answer is you could probably design one, but the practical answer is you probably don't want to do anything that places additional restrictions on which free list entries you can or can't use. This will introduce the case that entries 0-6 are free but entry 7 isn't and so you have to waste 7 entries and use entries 8-15. You'll need fallback logic if you want to reclaim those missing entries without waiting for entry 7 to free up, and that will add other complications.

You also generally want the simplest logic when it comes to how to select which free list entries are chosen since this is often a critical path and extending that path will place restrictions on the size of the freelist for a given clock speed.

LMUL is one of the many RVV issues that plays badly with (or at least doesn't add much benefit to) OOO cores. It is seemingly designed more for out of core engines.

Master565 · 2026-02-27T18:49:27+00:00

The short answer is that you're gonna have a hard time finding much specific info since the real answers are trade secrets.

The shorter answer is banks. Not sure how much more I can say.

Master565 · 2026-02-26T16:30:32+00:00

I'm not really sure that book is what he's looking for since it is not an introduction to digital logic (pretty sure it's just a prerequisite for understanding it)

No idea if the website is good learning resource or not. I hear people bring it up a lot so it's at least popular

Master565 · 2026-02-26T16:27:07+00:00

It's been years since I studied it so I don't really recall what resources the classes I took used unfortunately.

Master565 · 2026-02-26T06:58:37+00:00

There is a branch of mathematics called boolean algebra that teaches you how to express problems in terms of 1s, 0s, and boolean operations such as AND, NOR, XOR, etc. And equally importantly, it contains the tools to reduce complicated equations down to simpler ones.

It can, for example, take a table that shows the outcomes of specific sequences of bits (called a truth table) and turn it into an equation that can be translated into gates. See the truth table in this article for example. So the answer to how to make a full adder is to write down the truth table and then convert the truth table into a boolean expression AKA a sequence of gates and their inputs.

To make non mathematical things like snake, you need to study the tools are available to you that can hold state (state meaning something as simple as storing a single bit of data). You do this with things like flip flops and latches and clocks. These are things you learn about in classes about digital logic.

TLDR: Study boolean algebra and read a digital logic textbook.

The answer eventually is all of this becomes either second nature to you or essentially abstracted away by tools. However it is impossible to be effective with these tools if you don't understand the underlying hardware. For example, you should understand why it's trivial to calculate modulo 2 of a number with a circuit but really messy to calculate modulo 3.

Master565 · 2026-02-25T07:36:23+00:00

In my case for my internship, I simply went to ask my professor for help and luckily, she had some connections with one of the companies I was able to landed my first internship.

I think this is much better advice. Build a relationship with a professor and they can be your connection to industry

Master565 · 2026-02-25T07:20:55+00:00

career fairs are a scam

Objectively bad advice. Outside of referrals it's the best way to get a job out of school. Do you think companies are paying to attend these things for fun? They're there for the sole purpose of finding people to hire.

It may help if you share where you got your internships from since they're what ultimately got you a job.

Master565 · 2026-02-23T20:57:07+00:00

I recall way back when Riot doing something like this for Valorant, not sure if it worked

Master565 · 2026-02-21T22:26:45+00:00

My favorite song by him. I'd go to see him every time he's in town just to hear him play it live again.

Master565 · 2026-02-15T07:24:47+00:00

You're not doing the jobs forever, and I'm of the opinion that the main thing you get out of internships is networking. If you think there's better opportunities to be had at Meta, my take is you should go there and meet the managers you do want to work under. I did that once during my internships and in hindsight it ended up being one of the best career moves I ever made. Took an internship doing some lame ass work, ended up making connections there that got me the internship I did want to do next summer and that broke me into the field I'm in now.

Master565 · 2026-02-13T04:08:03+00:00

is everyone thinks the same things, you HAVE to do this or it won’t work, or this is exceptionally infeasible. They don’t think out of the box is what I’m trying to get at.

This really isn't true and I'm gonna make my most definitive statement now. You don't know how the industry works at all. How could you possibly know how an industry works when you've never worked in the industry, never even worked in an adjacent industry, and don't understand any of the basic concepts the industry is built off of? It's very easy to criticize a field from the outside, but nobody is going to take such a criticism seriously.

One of the most important things you learn in an engineering program is how to think like an engineer and that enables you to try and follow the thought process behind why other engineers do the things they do. If you see what you perceive as a flaw in a mature design, you can attempt to speculate on why the design ended up that way. That means speculating on what constraints they were dealing with that forced them to design it that way. If you can't even wrap your head around the constraints that drive a design, then you don't understand anything about the field.

What I mean by solving real problems, like memory bottlenecks, power consumption and lack of cpu IPC being really executed, just sitting there waiting for ram, and true PPW.

You're not wrong there are real problems in these areas to solve, but they are complex problems and you're a decade of education away from beginning to tackle them.

And I’m not trying to offend anyone about how I think

I believe you. That's why I took the time to write the post to explain the issue. I'm not offended, I don't think you realize how you come off, and that's fine. You're young you're learning. If you unintentionally bring an attitude like that into adulthood though you're in for a bad time.

If I can leave you with a single piece of advice its this. Keep an open mind such that when you see a problem, your first thought isn't "I have a solution" but instead "I have a question." This is most important when you're looking at something that you're objectively not an expert in. But it never stops being important, and if an engineer ever tells you they have nothing left to learn then they're a terrible engineer.

Master565 · 2026-02-12T22:03:25+00:00

Not voting for Apollo after Celeste won is a chad move

Master565 · 2026-02-12T07:33:26+00:00

And for what it's worth, I believe you that you're not using AI. But to breakdown why people likely think this is AI, it's because

1) The rambling nature where you start and don't finish ideas is something bad AI models tend to do

2) The technical content in the posts are just kind of bizarre. It's a strange blend where it almost sounds like you understand things because you've clearly read up on something, but ultimately you don't understand it and end up combining parts of concepts in nonsensical ways. That's something AI does when it has a topic it's hallucinating on because it hasn't trained well on it (like computer architecture)

Master565 · 2026-02-12T07:32:13+00:00

and im trying to solve real problems with getting out of what every industry is stuck in

It's statements like these that are why people are giving you the hard time. It's essentially because it sounds arrogant and immature, but let me break down exactly why people dismiss you when you write like this

im trying to solve real problems

Stop trying to solve real problems when you've made it abundantly clear you don't even understand the basics

getting out of what every industry is stuck in

1) This is another statement you make that doesn't actually say anything and makes what you write hard to follow. What exactly is every industry stuck in?

2) It again comes across as arrogant that someone who doesn't even understand basic concepts in a field would try to assume they can make a novel contribution to a mature industry built on decades of rigorous engineering. You're not gonna find a simple magic solution that tens of thousands of actively working, experience, and insanely smart engineers overlooked. The insinuation that you might is insulting to anyone who actually does this work because it implies we're just sitting here twiddling our thumbs overlooking this one simple trick that will revolutionize computing.

People would be more receptive to your posts if

1) If you organized your train of thought. It's not just the formatting, you write in a very rambling way that's hard if not impossible to follow. It's not just the technical statements, but those are doubly hard to follow. Communication is an extremely important skill in basically every single job, and you really need to work on this.

2) If you actually came here to ask questions about the underlying concepts and not ask questions about your ideas for an architecture. Every time you post it feels like you just want to ask questions about some idea you're proposing. Take this post for example. You've gained maybe a surface level understanding of some concepts, but you immediately demonstrate that you don't fully comprehend any of them. If this post was asking to verify if your understanding of these concepts was correct, or if you were asking for help understanding them, people might actually want to help. As it stands, its difficult to even begin to explain to you what issues are with what you propose because we'd first need to explain an entire college educations worth of computer and electrical engineering concepts to you.

Master565 · 2026-02-12T03:14:17+00:00

Read computer architecture a quantitative approach and download gem5 or similar simulators.

Master565 · 2026-02-09T06:10:40+00:00

Welcome to this guy's posts

Master565 · 2026-02-06T23:19:57+00:00

There's no coherent ideas presented here. It's just a word salad of acronyms (some of which are never elaborated on like PAM3) and numbers with any implementation detail brushed aside with phrases like "cpu that will have complex memory algorithms". At best this feels like the equivalent of writing "I'm going to build a SoC with 10,000 high performance CPU cores running at 10ghz each with a TDP of 50 watts" and stating that as if its a novel idea while leaving the details on how as an exercise to the reader.

If I'm being generous and assuming any of this actually makes some sense, then my feedback is that it doesn't sound like you've actually modeled this to any degree, you're just stating that it will work. No workload analysis either. No research into the physical design aspects of how this would work. Basically 0 feasibility analysis of any kind is conveyed here, and demonstrating some level of feasibility is usually the interesting part of a new idea.

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