Latency Numbers Every Programmer Should Know

latency.txt

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
------
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

以讹传讹，有个数据明显不对..

Wondering which chips and OS are you using here to calculate that latency

Send 1K bytes over 1 Gbps network

1Gbps is a measure of bandwidth and is irrelevant to latency

@Hawzen

1Gbps is a measure of bandwidth and is irrelevant to latency

1Gbps = 1,000,000,000 bits/sec
1KB = 1024 bytes = 1024 x 8 = 8192 bits
8192 bits / 1,000,000,000 bps = 0.00000819 seconds (aka 8.192 µs, or 8192 ns)

That's before TCP, IPv4, Ethernet headers and other framing on the wire -- not quite 10,000 ns but close enough.

Stuart Cheshire's Latency and the Quest for Interactivity paper is still excellent 30 years later. It digs into serialization delays a fair bit (albeit with much smaller numbers). Well worth a read.