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Latency numbers every programmer should know

https://cheat.sh/latency
27•ksec•4h ago

Comments

sneilan1•2h ago
Does anyone have Jeff Dean's sources for how he computed these numbers? What's the margin of error? How accurate are they now? Is there a set of numbers that also talks about memory bandwidth in GPUs? Are these numbers intel/amd only? How do they differ between an m1 architecture?
kgwxd•2h ago
It raises so many questions. The only one I want the answer to is: Will these numbers help me reach the Doherty threshold?
whynotmaybe•45m ago
For the uninitiated like me :

> Productivity soars when a computer and its users interact at a pace (<400ms) that ensures that neither has to wait on the other.

https://lawsofux.com/doherty-threshold/

checker659•2h ago
Can we also add: RDMA (RoCEv2) : ~2.5us
kgwxd•1h ago
I don't think these numbers mean much to me but, I didn't know this site existed. What an excellent idea.
yomismoaqui•1h ago
> Send 2,000 bytes over commodity network: 5ns

Shouldn't this be 5µs?

vitus•1h ago
Well, it shouldn't be slower than "Read 1,000,000 bytes sequentially from memory" (741ns) which in turn shouldn't be slower than "Read 1,000,000 bytes sequentially from disk" (359 us).

That said, all those numbers feel a bit off by 1.5-2 orders of magnitude -- that disk read speed translates to about 3 GB/s which is well outside the range of what HDDs can achieve.

https://brenocon.com/dean_perf.html indicates the original set of numbers were more like 10us, 250us, and 30ms.

And it links to https://github.com/colin-scott/interactive_latencies which seems like it extrapolates progress from 14 years ago:

        // NIC bandwidth doubles every 2 years
        // [source: http://ampcamp.berkeley.edu/wp-content/uploads/2012/06/Ion-stoica-amp-camp-21012-warehouse-scale-computing-intro-final.pdf]
        // TODO: should really be a step function
        // 1Gb/s = 125MB/s = 125*10^6 B/s in 2003
which means that in 2026 we'll have seen 11 doublings since gigabit speeds in 2003, so we'll all have > terabit speeds available to us.
yomismoaqui•1h ago
You are right, but my comment was about a trivial observation: 1 green square is 10µs so half a green square should be 5µs (not 5ns)

So I guess it's a typo but it makes me doubt the other numbers.

amluto•36m ago
> that disk read speed translates to about 3 GB/s which is well outside the range of what HDDs can achieve.

That’s PCIe 3.0 x4 or PCIe 4.0 x2, which a decent commodity M.2 NVMe SSD can use and can possibly saturate, at least for reads.

> which means that in 2026 we'll have seen 11 doublings since gigabit speeds in 2003, so we'll all have > terabit speeds available to us.

We’re not that far off. 100GbE hardware is not especially expensive these days. Little “AI” boxes with 400-800 Gbps of connectivity are a thing.

That being said, all the connections over 100Gbps are currently multi-lane AFAIK, and the heroic efforts and multiplexing needed to exceed 100Gbps at any distance are a bit in excess of the very simple technology that got us to 100Mbps “fast Ethernet”.

Zambyte•1h ago
This graph is also very helpful

http://ithare.com/infographics-operation-costs-in-cpu-clock-...

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Latency numbers every programmer should know

https://cheat.sh/latency
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