everyone should know time latency
字数1485 2021-08-20T17:30:55

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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