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Last active December 12, 2024 08:18
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Latency Numbers Every Programmer Should Know
Latency Comparison Numbers (~2012)
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L1 cache reference 0.5 ns
Branch mispredict 5 ns
L2 cache reference 7 ns 14x L1 cache
Mutex lock/unlock 25 ns
Main memory reference 100 ns 20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy 3,000 ns 3 us
Send 1K bytes over 1 Gbps network 10,000 ns 10 us
Read 4K randomly from SSD* 150,000 ns 150 us ~1GB/sec SSD
Read 1 MB sequentially from memory 250,000 ns 250 us
Round trip within same datacenter 500,000 ns 500 us
Read 1 MB sequentially from SSD* 1,000,000 ns 1,000 us 1 ms ~1GB/sec SSD, 4X memory
Disk seek 10,000,000 ns 10,000 us 10 ms 20x datacenter roundtrip
Read 1 MB sequentially from disk 20,000,000 ns 20,000 us 20 ms 80x memory, 20X SSD
Send packet CA->Netherlands->CA 150,000,000 ns 150,000 us 150 ms
Notes
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1 ns = 10^-9 seconds
1 us = 10^-6 seconds = 1,000 ns
1 ms = 10^-3 seconds = 1,000 us = 1,000,000 ns
Credit
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By Jeff Dean: http://research.google.com/people/jeff/
Originally by Peter Norvig: http://norvig.com/21-days.html#answers
Contributions
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'Humanized' comparison: https://gist.github.com/hellerbarde/2843375
Visual comparison chart: http://i.imgur.com/k0t1e.png
Interactive Prezi version: https://prezi.com/pdkvgys-r0y6/latency-numbers-for-programmers-web-development/latency.txt
@josephjoeljo
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One more thing I gotta memorize 😔

@vbansal2
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vbansal2 commented Oct 25, 2024

Let's use 🍌 for the scale 👉

Operation Time (ns) Banana Units
L1 cache reference 0.5 ns 1 banana (one banana)
Branch mispredict 5 ns 10 bananas (ten bananas)
L2 cache reference 7 ns 14 bananas (fourteen bananas)
Mutex lock/unlock 25 ns 50 bananas (fifty bananas)
Main memory reference 100 ns 200 bananas (two hundred bananas)
Compress 1K bytes with Zippy 3,000 ns 6,000 bananas (six thousand bananas)
Send 1K bytes over 1 Gbps network 10,000 ns 20,000 bananas (twenty thousand bananas)
Read 4K randomly from SSD 150,000 ns 300,000 bananas (three hundred thousand bananas)
Read 1 MB sequentially from memory 250,000 ns 500,000 bananas (five hundred thousand bananas)
Round trip within same datacenter 500,000 ns 1,000,000 bananas (one million bananas)
Read 1 MB sequentially from SSD 1,000,000 ns 2,000,000 bananas (two million bananas)
Disk seek 10,000,000 ns 20,000,000 bananas (twenty million bananas)
Read 1 MB sequentially from disk 20,000,000 ns 40,000,000 bananas (forty million bananas)
Send packet CA->Netherlands->CA 150,000,000 ns 300,000,000 bananas (three hundred million bananas)

In this table, each operation's latency is expressed in terms of the smallest unit—a single L1 cache reference, which is equivalent to 1 banana.

@speculatrix
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while I find the idea of a banana as a base unit of distance, it's not really helpful here. however, you could do a scale of distances, starting at the planck length in femto bananas or something.

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