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Latency numbers every programmer should know

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
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
Round trip within same datacenter ...... 500,000 ns  = 0.5 ms
Read 1 MB sequentially from SSD* ..... 1,000,000 ns  =   1 ms
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

Assuming ~1GB/sec SSD

Visual representation of latencies

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 it takes to complete a bachelor's degree
@toelke
toelke commented May 31, 2012

25s is making one coffee. 7.8 months is a tad faster than producing a new human being. One disk-seek (16 weeks) and then reading 1MiB (7.8 months) is one year.

@hellerbarde
Owner

thx, will incorporate those!

@Smerity
Smerity commented May 31, 2012

16.5 weeks ~= four months ~= full semester at university ~= summer break ?

@drbawb
drbawb commented May 31, 2012

branch mis-predict: a yawn.

Such an accurate portrayal. "yawwwn aw damn it fell through to the else again."

@dleonard0

4.8 years is very roughly two round trips to Mars. Or a one-way trip to Europa.

@mshock
mshock commented Jun 1, 2012

neat, thanks!

@henrik
henrik commented Jun 1, 2012

4.8 years is about how long a bachelor's degree takes on average (4.7 years in 2008 according to this page).

@stephan-buckmaster

Should add date of creation to text itself (as of ...)

@bartmcleod

If enough people start reading this, the last one will have to wait several years

@colin-scott

Here's a tool to visualize these numbers over time: http://www.eecs.berkeley.edu/~rcs/research/interactive_latency.html

@miraculixx

Great interactive chart! Suggest to add CPU cycles for a simple single instructions such as ADD, MOV, MULT (e.g. "multiplying two 16bit integers".

@legrady
legrady commented Jan 10, 2013

I'd like to see a duration for function-call overhead. Late 80s when I was in school, it was several micro-seconds, enough that people had concerns about having unnecessary function calls. I'm sure that doesn't apply any more, but I don't have real numbers.

@milesrout

@legrady it depends on a lot of factors. Is it a virtual function call?

@smchild
smchild commented Aug 18, 2014

大神

@AdamBSteele

If reading 1MB from an SSD costs 1ms, what would the cost be to read 10MB sequentially from an SSD?

@b1nary
b1nary commented Dec 8, 2014

This is a great collection. I just dont get where or how i am able to make coffee in just 25s.

@stultus
stultus commented Dec 8, 2014

Agree @b1nary . if someone knows how to do that, please share the source code :smile:

@jeveloper

That would be a shocker if devops status page turned into humanized numbers one day (sometime in april).
We should all start working harder to improve our numbers ! and enjoy more Round trip within same datacenter :smiley:

@benibela
benibela commented Dec 8, 2014

Do not forget:

3ms: Time till a wrongly configured sendmail timeouts and fails to deliver a mail. Roughly corresponds to mail servers in a 500km (3 millilightseconds) radius

6h: Time to send a mail across those 500km via RFC 1149

@caimaoy
caimaoy commented Jan 5, 2015

cool

@hellerbarde
Owner

@stultus @b1nary we have a coffee machine that makes coffee. Ta-Dah! :smile:

@GreatmanBill

good, it's cool!

@villadora

cool! great summary

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