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Latency Numbers Every Programmer Should Know
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Latency Comparison Numbers (~2012) | |
---------------------------------- | |
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 | |
----- | |
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 | |
------ | |
By Jeff Dean: http://research.google.com/people/jeff/ | |
Originally by Peter Norvig: http://norvig.com/21-days.html#answers | |
Contributions | |
------------- | |
'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 |
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.
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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One more thing I gotta memorize 😔