How much linear memory access is enough?
55 points
3 days ago
| 5 comments
| solidean.com
| HN
smj-edison
15 minutes ago
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Side note, but this product looks really cool! I have a fundamental mistrust of all boolean operations, so to see a system that actually works with degenerate cases correctly is refreshing.
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PhilipTrettner
3 days ago
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I looked into this because part of our pipeline is forced to be chunked. Most advice I've seen boils down to "more contiguity = better", but without numbers, or at least not generalizable ones.

My concrete tasks will already reach peak performance before 128 kB and I couldn't find pure processing workloads that benefit significantly beyond 1 MB chunk size. Code is linked in the post, it would be nice to see results on more systems.

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twoodfin
5 hours ago
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Your results match similar analyses of database systems I’ve seen.

64KB-128KB seems like the sweet spot.

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aapoalas
18 minutes ago
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Would kernel huge pages possibly have an effect here also?
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_zoltan_
3 hours ago
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is this an attempt at nerd sniping? ;-)

on GPU databases sometimes we go up to the GB range per "item of work" (input permitting) as it's very efficient.

I need to add it to my TODO list to have a look at your github code...

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PhilipTrettner
2 hours ago
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It definitely worked on myself :)

Do have a look, I've tried to roughly keep it small and readable. It's ~250 LOC effectively.

Also, this is CPU only. I'm not super sure what a good GPU version of my benchmark would be, though ... Maybe measuring a "map" more than a "reduction" like I do on the CPU? We should probably take a look at common chunking patterns there.

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01HNNWZ0MV43FF
44 minutes ago
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This is good data, but I'm not sure what the actionable is for me as a Grug Programmer.

It means if I'm doing very light processing (sums) I should try to move that to structure-of-arrays to take advantage of cache? But if I'm doing something very expensive, I can leave it as array-of-structures, since the computation will dominate the memory access in Amdahl's Law analysis?

This data should tell me something about organizing my data and accessing it, right?

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