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Bad benchmarks and evals: Senior SWE-Bench, napkin math, and winter tires

read original get Bridgestone Blizzak WS90 Winter Tires → more articles
Why This Matters

A widely-cited resource (the 5.4k-star napkin-math repo) is being used by engineers to prep for performance interviews, and this piece argues its numbers — alongside popular AI model evals like Senior SWE-Bench and even car tire tests — don't hold up on inspection. That matters because these benchmarks quietly shape hiring decisions, engineering intuition, model rankings, and consumer purchases. Popularity and star counts are not a proxy for accuracy.

Key Takeaways
Worth a Look

Bridgestone Blizzak WS90 Winter Tires — The article's detour into tire benchmarks is a good reminder that real-world winter grip is measured on ice and snow, not marketing copy — and the Blizzak line is the classic benchmark-setter in dedicated winter rubber. A set swapped on for the cold season transforms braking and cornering confidence compared to all-seasons. Just check your vehicle's tire size before ordering.

See Bridgestone Blizzak WS90 Winter Tires on Amazon → Affiliate link — we may earn a commission on purchases, at no extra cost to you. Product picked by AI based on this article; it is not a tested recommendation.

We're going to look at three different kinds of benchmarks, one set of calculations for baseline numbers for performance "napkin math" estimates, one set of AI model evals, and one on car tires. To build my intuition for things, I like thinking about them before seeing the explanation, so these are presented with the benchmark information first and the explanation later in case you want to think about your answer before seeing my thoughts.

29. A friend of mine is reviewing performance orders of magnitude to prep for computer performance interviews and found that https://github.com/sirupsen/napkin-math (5.4k stars) was the top hit. The README's tables include:

Napkin Math performance estimates Operation Latency Throughput 1 MiB 1 GiB Sequential Memory R/W (64 bytes) 0.5 ns ├ Single Thread 20 GiB/s 50 μs 50 ms ├ Threaded 200 GiB/s 5 μs 5 ms Network Same-Zone 10 GiB/s 100 μs 100 ms ├ Inside VPC 10 GiB/s 100 μs 100 ms ├ Outside VPC 3 GiB/s 300 μs 300 ms Hashing, not crypto-safe (64 bytes) 10 ns 5 GiB/s 200 μs 200 ms Random Memory R/W (64 bytes) 20 ns 3 GiB/s 300 μs 300 ms Fast Serialization [8] [9] † N/A 1 GiB/s 1 ms 1s Fast Deserialization [8] [9] † N/A 1 GiB/s 1 ms 1s System Call 300 ns N/A N/A N/A Hashing, crypto-safe (64 bytes) 100 ns 1 GiB/s 1 ms 1s Sequential SSD read (8 KiB) 1 μs 8 GiB/s 100 μs 100 ms Context Switch [1] [2] 10 μs N/A N/A N/A Sequential SSD write, -fsync (8KiB) 2 μs 3 GiB/s 300 μs 300 ms TCP Echo Server (32 KiB) 50 μs 500 MiB/s 2 ms 2s Random SSD Read (8 KiB) 100 μs 70 MiB/s 15 ms 15s Decompression [11] N/A 1 GiB/s 1 ms 1s Compression [11] N/A 500 MiB/s 2 ms 2s Sorting (64-bit integers) N/A 500 MiB/s 2 ms 2s Proxy: Envoy/ProxySQL/Nginx/HAProxy 50 μs ? ? ? Network within same region 250 μs 2 GiB/s 500 μs 500 ms Premium network within zone/VPC 250 μs 25 GiB/s 50 μs 40 ms Sequential SSD write, +fsync (8KiB) 300 μs 30 MiB/s 30 ms 30s {MySQL, Memcached, Redis, ..} Query 500 μs ? ? ? Serialization [8] [9] † N/A 100 MiB/s 10 ms 10s Deserialization [8] [9] † N/A 100 MiB/s 10 ms 10s Sequential HDD Read (8 KiB) 10 ms 250 MiB/s 2 ms 2s Random HDD Read (8 KiB) 10 ms 0.7 MiB/s 2 s 30m Blob Storage GET, if-not-match 304 30 ms Blob Storage GET, 1 conn (128KiB) 80 ms 100 MiB/s 10 ms 10s Blob Storage GET, n conn (offsets) 80 ms NW limit Blob Storage LIST 100 ms Blob Storage PUT, 1 conn (128KiB) 200 ms 100 MiB/s 10 ms 10s Blob Storage PUT, n conn (multipart) 200 ms NW limit 10 ms 10s Network between regions [6] Varies 25 MiB/s 40 ms 40s Network NA Central <-> East 25 ms 25 MiB/s 40 ms 40s Network NA Central <-> West 40 ms 25 MiB/s 40 ms 40s Network NA East <-> West 60 ms 25 MiB/s 40 ms 40s Network EU West <-> NA East 80 ms 25 MiB/s 40 ms 40s Network EU West <-> NA Central 100 ms 25 MiB/s 40 ms 40s Network NA West <-> Singapore 180 ms 25 MiB/s 40 ms 40s Network EU West <-> Singapore 160 ms 25 MiB/s 40 ms 40s Show full table

What's wrong with this benchmark?

30. I keep seeing people reference DeepSWE and Senior SWE-Bench to "prove" that their favorite model is better than other people's favorite models or just as generally good benchmarks, such as in

What's wrong with these benchmarks?

31. People frequently say that winter tires are superior to all-season tires in cold weather. For example, on googling "all season tires during winter cold" (no quotes), the Google AI summary leads with

All-season tires lose traction and stiffen in freezing winter temperatures. Their rubber compounds are designed for warmer weather and become hard below 7°C (45°F), leading to significantly longer braking distances and reduced grip ... The rubber in all-season tires cannot maintain pliability in sub-zero temperatures, causing them to perform more like hard plastic on snow and ice.

Given that there are a lot of internet comments in the training data, this is a reasonable comment, in that I frequently see variations on this comment on discussions of which tires one should use.

What's wrong with this benchmark?

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