iiinova — where your digital self keeps evolving

Abhinav Upadhyay @abhi9u.bsky.social · 16/05/2026

I wrote a 60-page mini-book on Virtual Memory. Going from what it is, through page tables and down to advanced topics like copy-on write, demand paging, TLB shootdowns, NUMA placement, page reclamation algorithms. blog.codingconfessions.com/p/virtual-me...

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Abhinav Upadhyay @abhi9u.bsky.social · 22/12/2025

I recently explored how DL frameworks leverage the parallel cores in the GPU to generate random numbers in parallel.

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Abhinav Upadhyay @abhi9u.bsky.social · 21/09/2025

System calls are the interface between the user space and the kernel. They are needed for fundamental things like reading a file, and making a network call. But they are also very expensive because they need to do things like saving/restoring registers, page table, stack.

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Teiva Harsanyi @teivah.dev · 16/09/2025

What Makes System Calls Expensive: A Linux Internals Deep Dive. blog.codingconfessions.com/p/what-makes... Another great post by @abhi9u.bsky.social. I learned a lot, including vDSO.

blog.codingconfessions.com

What Makes System Calls Expensive: A Linux Internals Deep Dive

An explanation of how Linux handles system calls on x86-64 and why they show up as expensive operations in performance profiles

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Abhinav Upadhyay @abhi9u.bsky.social · 13/07/2025

People talk about profiling to find bottlenecks, but no one explains how to fix them. Many devs shoot in the dark and when the optimization backfires, they aren't sure how to proceed.

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Abhinav Upadhyay @abhi9u.bsky.social · 21/05/2025

Skipping computer architecture was my biggest student mistake. Hardware’s execution model dictates memory layout, binaries, compiler output, and runtimes. If you want to build systems, learn how the CPU works. I wrote an article on this: blog.codingconfessions.com/p/seeing-the...

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Abhinav Upadhyay @abhi9u.bsky.social · 12/04/2025

Here’s a fun visual showing how len() finds the length of a list in Python. The size is stored right inside the object, but len() takes a five-pointer detour, only to land back where it started. This is why if not mylist is ~2x faster for emptiness checks!

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Abhinav Upadhyay @abhi9u.bsky.social · 28/03/2025

When you see an expert optimize a piece of code, it may look like dark magic. In reality, these experts have a deep understanding of the entire computing stack, and when they look at an application profile, they quickly understand the bottlenecks.

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Abhinav Upadhyay @abhi9u.bsky.social · 19/01/2025

How do you fit a 250kB dictionary in 64kB of RAM and still perform fast lookups? For reference, even with gzip -9, you can't compress this file below 85kB. In the 1970s, Douglas McIlroy faced this exact challenge while implementing the spell checker for Unix at AT&T.

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Suvash Thapaliya @suva.sh · 24/03/2025

The second post is by @abhi9u.bsky.social on some common CPU architecture concepts (instruction pipelining, memory caching &speculative execution). Abhi has done a great job with the analogies in this one. blog.codingconfessions.com/p/hardware-a...

blog.codingconfessions.com

Hardware-Aware Coding: CPU Architecture Concepts Every Developer Should Know

Write faster code by understanding how it flows through your CPU

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Teiva Harsanyi @teivah.dev · 21/03/2025

Hardware-Aware Coding: CPU Architecture Concepts Every Developer Should Know blog.codingconfessions.com/p/hardware-a... Another great post by @abhi9u.bsky.social

blog.codingconfessions.com

Hardware-Aware Coding: CPU Architecture Concepts Every Developer Should Know

Write faster code by understanding how it flows through your CPU

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Abhinav Upadhyay @abhi9u.bsky.social · 17/02/2025

Every few years linux distributions decide that they need to make it more difficult for you to generate and find core dump files. Now you need to install a systemd utility to do this.

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Abhinav Upadhyay @abhi9u.bsky.social · 05/02/2025

Woke up to an email from Douglas Mcilroy himself in response to my article on his work on Unix Spell. I am very grateful that he took the time to read and respond to it! PS: I fixed the error he found in the article. Article: blog.codingconfessions.com/p/how-unix-s...

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Abhinav Upadhyay @abhi9u.bsky.social · 19/01/2025

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Abhinav Upadhyay @abhi9u.bsky.social · 05/01/2025

Some old papers are a joy to read because of their simplicity. This is the abstract from a 1966 paper describing a compression technique for infinite codes. For static data, you know the probabilities of the symbols, and can build a Huffman tree, but for an infinite stream, you can't do that

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Codetoday Unlimited @codetodayunlimited.com · 02/01/2025

Back to school, time for Free Python Coding Resources for Schools, and by resources we mean our entire curriculum, all video lessons Help us spread the word with school teachers everywhere 50+ hours of lessons covering all levels, beginner to advanced, designed specifically for school children …👇🏻

Anime-style cartoon of teenage boy with headphones sitting at his laptop

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Abhinav Upadhyay @abhi9u.bsky.social · 02/01/2025

I noticed that my latest article trending on HN! So it's worth sharing here as well. It is first in a series to cover the internals of context switching in Linux. This one explains the core data structures for process and state management during context switching.

blog.codingconfessions.com

Linux Context Switching Internals: Part 1 - Process State and Memory

How does the Linux kernel represent processes and their state: A breakdown of task_struct and mm_struct

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Abhinav Upadhyay @abhi9u.bsky.social · 27/12/2024

An article I wrote a while back was trending on HN today. It explains the impossibility theorem of clustering, according to which a perfect clustering algorithm is impossible to achieve.

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Abhinav Upadhyay @abhi9u.bsky.social · 26/12/2024

You thought systems programmers don't need to know math? Linux kernel developers prove you wrong by contradiction—they prove corollaries in their comments.

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Sam Rose @samwho.dev · 20/12/2024

What does it mean for something to be Turing complete? I answer this question, and more, through a series of fully interactive Turing machine simulations! Play, pause, step forwards and backwards, and even write your own Turing machine programs in my latest blog post. samwho.dev/turing-machi...

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Abhinav Upadhyay @abhi9u.bsky.social · 20/12/2024

Continuing on the hardware concurrency thread, this paper is a must read. It simplifies reasoning about concurrency on x86 by providing an abstract machine model

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Abhinav Upadhyay @abhi9u.bsky.social · 08/12/2024

What every systems programmer should know about concurrency—a very dense but impactful read. Things like lock free and wait free synchronisation techniques will stop seeming like black box if you understand this. PDF: assets.bitbashing.io/papers/concu...

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Abhinav Upadhyay @abhi9u.bsky.social · 07/12/2024

Ulrich Drepper is a rockstar. I keep running into his papers. This one is on the implementation of thread local storage: PDF: www.akkadia.org/drepper/tls....

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Reposted by Abhinav Upadhyay

Shriram Krishnamurthi @shriram.bsky.social · 02/12/2024

Sometimes it takes me 22 years (+ one evening) to write a blog post. Here are my thoughts on "homoiconicity" and, as an alternative, "bicameral syntax". (Warning: 4000 words.) parentheticallyspeaking.org/articles/bic...

parentheticallyspeaking.org

Bicameral, Not Homoiconic

Parenthetically Speaking: Articles by Shriram Krishnamurthi

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Abhinav Upadhyay @abhi9u.bsky.social · 27/11/2024

When you first learn about the fork() syscall, it can seem magical. How can a single system call produce two different return values at the same time?! In my latest article, I demystify the hidden magic of fork and also show how it is implemented in Linux. blog.codingconfessions.com/p/the-magic-...

blog.codingconfessions.com

Disillusioning the Magic of the fork System Call

How the kernels implement the fork system call

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Abhinav Upadhyay @abhi9u.bsky.social · 21/11/2024

Hacking on some code while Cooper is occupied watching a movie.

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Abhinav Upadhyay @abhi9u.bsky.social · 20/11/2024

Recently, I discovered a hidden Easter egg inside Cpython and I wrote a very short post about it which is trending in a few forums. blog.codingconfessions.com/p/cpython-hi...

blog.codingconfessions.com

An Unreachable Hidden XKCD Easter Egg inside CPython

No, I'm not talking about import antigravity

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Abhinav Upadhyay @abhi9u.bsky.social · 19/11/2024

Ben Affleck's interview on his views on LLMs is going around. I wonder if Matt Damon is somewhere saying this to someone:

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Reposted by Abhinav Upadhyay

Stephen Gruppetta @stephengruppetta.com · 16/11/2024

I felt I needed to do something to keep my reputation as "The Turtle Guy"—funnily enough, I rarely post about `turtle`, but when I do, people seem to notice… Anyway, for the latest article on The Python Coding Stack, I revisited an old project… www.thepythoncodingstack.com/p/python-tur...

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Abhinav Upadhyay @abhi9u.bsky.social · 17/11/2024

A while back I published a detailed code walkthrough of CPython's GC implementation. But there was a need for a higher level explanation of the overall memory management mechanism of CPython without discussing the code. I did just that in a recent article. Here's a summary:

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Abhinav Upadhyay @abhi9u.bsky.social · 14/11/2024

Are there people here working in compilers or computer architecture space? Would love to diversify my feed. These are the two areas I'm primarily diving into these days. I'm not an expert, but I'm trying to build some fluency in these topics.

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Abhinav Upadhyay @abhi9u.bsky.social · 13/11/2024

Found this Easter egg in the CPython code today. As I looked at it I wondered who is Randall? Is he someone like David Beazely for whom special code was added. Mystery unravelled when reached the last line and found the xkcd reference :)

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Abhinav Upadhyay @abhi9u.bsky.social · 12/11/2024

My dog is turning into quite an actor

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Abhinav Upadhyay @abhi9u.bsky.social · 11/11/2024

I wrote an article on why the Pythonic way of checking a list for emptiness is not ambiguous. Whenever that is the case, there are ambiguities surrounding it which can make it look ambiguous as well. blog.codingconfessions.com/p/the-python...

blog.codingconfessions.com

The Pythonic Emptiness

Why the Pythonic way of doing emptiness check on sequences is not necessarily ambiguous in most cases

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Abhinav Upadhyay @abhi9u.bsky.social · 04/11/2024

The X86 instruction encoding is atrocious. How does the CPU even decode it?!

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Abhinav Upadhyay @abhi9u.bsky.social · 04/11/2024

The Linux kernel has a JIT compiler for compiling the bytecode of BPF programs into machine code. How does it work?

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Abhinav Upadhyay @abhi9u.bsky.social · 02/11/2024

Love this (new?) fish feature. On doing <Tab> with a partially written man page name, the autocomplete also shows a description of the suggested man pages so I can quickly tell which one I want to look up

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Abhinav Upadhyay @abhi9u.bsky.social · 02/11/2024

Aligning up or down to a power-of-2 boundary is a very common operation. I've seen many people use the % operator to do it. But there is a more efficient way of doing it in just 2 instructions.

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Abhinav Upadhyay @abhi9u.bsky.social · 30/10/2024

Brendan Gregg has been busy. He is now trying to build full stack profiling for GPU kernels, i.e., flame graphs which show all the code right from the CPU down to the last bit of kernel code running on the GPU. He calls it AI flame graphs. It seems he has it ready for the Intel GPUs.

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Abhinav Upadhyay @abhi9u.bsky.social · 27/10/2024

While most compiler courses and books currently teach parsing algorithms from the 70s and 80s, CPython uses a parsing technique published in 2004 and which is still not taught widely.

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Abhinav Upadhyay @abhi9u.bsky.social · 25/11/2023

In the past, I've written a few articles on cpython internals. It's a topic I enjoy a lot and plan to cover more. My latest piece covers a fundamental idea in cpython implementation which underlies the object system codeconfessions.substack.com/p/cpyt…

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Abhinav Upadhyay @abhi9u.bsky.social · 03/11/2023

One of the rare days I had a chance to refer to this for something I'm working on

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Abhinav Upadhyay @abhi9u.bsky.social · 19/10/2023

If you wondered why GPUs are in so much demand and how do they work, then I've got you covered. What Every Developer Should Know About GPUs: codeconfessions.substack.com/p/gpu-…

codeconfessions.substack.com

What Every Developer Should Know About GPU Computing

A primer on GPU architecture and computing

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