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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

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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

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Owner

hellerbarde commented May 31, 2012

thx, will incorporate those!

@Smerity

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Smerity commented May 31, 2012

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

@drbawb

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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

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dleonard0 commented Jun 1, 2012

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

@mshock

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mshock commented Jun 1, 2012

neat, thanks!

@henrik

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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

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stephan-buckmaster commented Jun 4, 2012

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

@bartmcleod

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bartmcleod commented Jun 26, 2012

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

@colin-scott

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colin-scott commented Dec 25, 2012

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

@miraculixx

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miraculixx commented Dec 27, 2012

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

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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

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milesrout commented Jun 19, 2014

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

@coolearn

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coolearn commented Aug 18, 2014

大神

@AdamBSteele

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AdamBSteele commented Dec 8, 2014

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

@b1nary

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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

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stultus commented Dec 8, 2014

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

@jeveloper

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jeveloper commented Dec 8, 2014

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 😃

@benibela

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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

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caimaoy commented Jan 5, 2015

cool

@hellerbarde

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Owner

hellerbarde commented Apr 24, 2015

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

@GreatmanBill

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GreatmanBill commented Apr 28, 2015

good, it's cool!

@villadora

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villadora commented Apr 15, 2016

cool! great summary

@susingha

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susingha commented Oct 9, 2016

this is awesome. Thank you

@marianposaceanu

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marianposaceanu commented Oct 9, 2016

hmm:

branch misprediction penalty on Haswell ~ 1500 ns vs 5 ns in the gist. That's three orders of magnitude of error

EDIT:

I used the ticks from Windows (are 10K in a ms) which is incorrect related to the gist.

If the Haswell CPU is running 3.6Ghz - one cycle would equal to 0.27ns that would mean a branch miss would be 4.05ns - seems about right now.

@PatelParas

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PatelParas commented Oct 11, 2016

cool..... thank you

@Kevin-Hamilton

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Kevin-Hamilton commented Oct 11, 2016

Multiplying by a billion stretches the timescales out too much for my taste. So I came up with an alternate list based on multiplying by only 22,000:

L1 cache reference ..................  0.000011 seconds (SR-71 travels 1cm)
Branch mispredict ...................  0.000110 sec (Bullet travels 4cm)
L2 cache reference ..................  0.000154 sec (Boeing 777 travels 4cm)
Mutex lock/unlock ...................  0.00055 sec (Time before you hear a fingersnap made in front of your face [speed of sound across 19cm])
Main memory reference ...............  0.0022 sec (Camera shutter on a sunny day [1/400 - 1/500 shutter speed])
Compress 1K bytes with Zippy ........  0.066 sec (Lightning bolt travels 4km from cloud to ground)
Send 2K bytes over 1 Gbps network ...  0.44 sec (Fastball from pitcher to home plate)
SSD random read .....................  3.3 sec (SR-71 travels 3.1km)
Read 1 MB sequentially from memory ..  5.5 sec (Yawn)
Round trip within same datacenter ... 11.0 sec (A Cheetah runs 200m)
Read 1 MB sequentially from SSD* .... 22.0 sec (Usain Bolt runs 200m)
Disk seek ...........................  3.6 minutes (Brewing coffee in a French Press)
Read 1 MB sequentially from disk ....  7.3 min (A performance of the first movement of Beethoven's 5th Symphony)
Send packet CA->Netherlands->CA ..... 55.0 min (Going for a brisk 5km walk)
@MartyGentillon

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MartyGentillon commented Oct 12, 2016

@Kevin-Hamilton There is a reason to stretch it out that much. From a human perspective, it is really hard to do anything in less than a second. As such, the ridiculously long times give you a better idea of what a computer might be able to do during that disk seek, if it weren't waiting for that disk seek.

Because of this, most of the similar pages I have seen use something like 1 second for a clock cycle (so multiply everything there by 3 or 4). It gives a really good sense of machine sympathy.

@mpron

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mpron commented Oct 12, 2016

Last year, I came up with this concept for an infographic illustrating these latency numbers with time analogies (if 1 CPU cycle = 1 second). Here was the result (attached, and here's a link: http://imgur.com/8LIwV4C)pic

@cth027

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cth027 commented Nov 19, 2016

Excellent idea ! Great page !
Perhaps an interesting comparison:

@MAZHARMIK

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MAZHARMIK commented Dec 30, 2016

Cool. Loved it.

@hhimanshu

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hhimanshu commented Jan 22, 2017

very interesting!

@imonti

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imonti commented Mar 31, 2017

Excelent Gist.

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