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Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns                     on recent CPU
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 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs
Read 1 MB sequentially from memory ..... 250,000 ns  = 250 µs           4X memory
Round trip within same datacenter ...... 500,000 ns  = 0.5 ms           20x datacenter roundtrip
Read 1 MB sequentially from SSD* ..... 1,000,000 ns  =   1 ms           80x memory, 20X SSD
Disk seek ........................... 10,000,000 ns  =  10 ms
Read 1 MB sequentially from disk .... 20,000,000 ns  =  20 ms
Send packet CA->Netherlands->CA .... 150,000,000 ns  = 150 ms
LTO4 tape seek/access time ...... 55.000.000.000 ns  =  55 s

Assuming ~1GB/sec SSD

Visual representation of latencies

Evolution over Years Berkeley

Pings around the world WonderNetwork

PC Hardware Speeds Gustavo Duartes

Visual chart provided by ayshen

Data by Jeff Dean

Originally by Peter Norvig

Lets multiply all these durations by a billion:

Magnitudes:

Minute:

L1 cache reference                  0.5 s         One heart beat (0.5 s)
Branch mispredict                   5 s           Yawn
L2 cache reference                  7 s           Long yawn
Mutex lock/unlock                   25 s          Making a coffee

Hour:

Main memory reference               100 s         Brushing your teeth
Compress 1K bytes with Zippy        50 min        One episode of a TV show (including ad breaks)

Day:

Send 2K bytes over 1 Gbps network   5.5 hr        From lunch to end of work day

Week

SSD random read                     1.7 days      A normal weekend
Read 1 MB sequentially from memory  2.9 days      A long weekend
Round trip within same datacenter   5.8 days      A medium vacation
Read 1 MB sequentially from SSD    11.6 days      Waiting for almost 2 weeks for a delivery

Year

Disk seek                           16.5 weeks    A semester in university
Read 1 MB sequentially from disk    7.8 months    Almost producing a new human being
The above 2 together                1 year

Decade

Send packet CA->Netherlands->CA     4.8 years     Average time to complete a bachelor's degree

Latency numbers from Systems Performance book Scaled

CPU cycle .................................... 0.3 ns                 1 s
L1 cache reference ........................... 0.9 ns                 3 s
L2 cache reference ........................... 2.8 ns                 9 s
L3 cache reference .......................... 12.9 ns                43 s
Main memory access (DRAM, from CPU) .......... 120 ns                 6 min
SSD I/O (flash memory) .................... 50-150 µs               2-6 days
Rotational disk I/O ......................... 1-10 ms              1-12 months
Internet : San Francisco to New York ...........40 ms                 4 years
Internet : San Francisco to United Kingdom .... 81 ms                 8 years
Internet : San Francisco to Australia ........ 183 ms                19 years
TCP packet retransmit ........................ 1-3 s            105-317 years
OS virtualization system reboot ................ 4 s                423 years
SCSI command time-out ......................... 30 s                  3 millennia
Hardware virtualization system reboot ......... 40 s                  4 millennia
Physical system reboot ......................... 5 min               32 millennia

Assuming 3.3GHz CPU, ~1GB/sec SSD

Data by Brendan Gregg | Systems Performance book via @rzezeski

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