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@jboner
Last active December 5, 2024 05:13
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Latency Numbers Every Programmer Should Know
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
Interactive Prezi version: https://prezi.com/pdkvgys-r0y6/latency-numbers-for-programmers-web-development/latency.txt
@sirupsen
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sirupsen commented Jan 8, 2021

I've been doing some more work inspired by this, surfacing more numbers, and adding throughput:

https://github.com/sirupsen/napkin-math

@sachin-j-joshi
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Is there a 2021 updated edition?

@ellingtonjp
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ellingtonjp commented Apr 15, 2021

@sirupsen I love your project and I'm signed up for the newsletter. Currently making Anki flashcards :)

There are some large discrepancies between your numbers and the ones found here (not sure where these numbers came from):
https://colin-scott.github.io/personal_website/research/interactive_latency.html

I'm curious what's causing them. Specifically, 1MB sequential memory read: 100us vs 3us.

@sirupsen
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@ellingtonjp My program is getting ~100 us, and this one says 250 us (from 2012). Lines up to me with some increases in performance since :) Not sure how you got 3 us

@ellingtonjp
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ellingtonjp commented Apr 15, 2021

@sirupsen I was referring to the numbers here https://colin-scott.github.io/personal_website/research/interactive_latency.html

The 2020 version of "Read 1,000,000 bytes sequentially from memory" shows 3us. Not sure where that comes from though. Yours seems more realistic to me

@sirupsen
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sirupsen commented Apr 17, 2021

Ahh, sorry I read your message too quick. Yeah, unclear to me how someone would get 3us. The code I use for this is very simple. It took reading the x86 a few times to ensure that the compiler didn't optimize it out. I do summing, which is one of the lightest workloads you could do in a loop like that. So I think it's quite realistic. Maybe that person's script it was optimized out? 🤷

@ellingtonjp
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To everyone interested in numbers like this:

@sirupsen 's project is really good. He gave an excellent talk on the "napkin math" skill and has a newsletter with monthly challenges for practicing putting these numbers to use.

Newsletter: https://sirupsen.com/napkin/
Github: https://github.com/sirupsen/napkin-math
Talk: https://www.youtube.com/watch?v=IxkSlnrRFqc

@awsles
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awsles commented Jun 9, 2021

:)
Light to reach the moon 2,510,000,000 ns 2,510,000 us 2,510 ms 2.51 s

@invisiblethings
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invisiblethings commented Nov 24, 2021

Heh, imagine this transposed into human distances.

1ns = 1 step, or 2 feet.

L1 cache reference = reaching 1 foot across your desk to pick something up
Datacentre roundtrip = 94 mile hike.
Internet roundtrip (California to Netherlands) = Walk around the entire earth. Wait! You're not done. Then walk from London, to Havana. Oh, and then to Jacksonville, Florida. Then you're done.

@apimaker001
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useful information & thanks

@eduard93
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eduard93 commented Jan 3, 2022

What about register access timings?

@crazydogen
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crazydogen commented Apr 6, 2022

Markdown version :p

Operation ns µs ms note
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 µs
Send 1K bytes over 1 Gbps network 10,000 ns 10 µs
Read 4K randomly from SSD* 150,000 ns 150 µs ~1GB/sec SSD
Read 1 MB sequentially from memory 250,000 ns 250 µs
Round trip within same datacenter 500,000 ns 500 µs
Read 1 MB sequentially from SSD* 1,000,000 ns 1,000 µs 1 ms ~1GB/sec SSD, 4X memory
Disk seek 10,000,000 ns 10,000 µs 10 ms 20x datacenter roundtrip
Read 1 MB sequentially from disk 20,000,000 ns 20,000 µs 20 ms 80x memory, 20X SSD
Send packet CA -> Netherlands -> CA 150,000,000 ns 150,000 µs 150 ms

@LuisOsta
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@jboner What do you think about adding cryptography numbers to the list? I feel like that would be a really valuable addition to the list for comparison. Especially as cryptography usage increases and becomes more common.

We could for instance add Ed25519 latency for cryptographic signing and verification. In a very rudimentary testing I did locally I got:

  1. Ed25519 Signing - 254.20µs
  2. Ed25519 Verification - 368.20µs

You can replicate the results with the following rust program:

fn main() {
    println!("Hello, world!");
    let msg = b"lfasjhfoihjsofh438948hhfklshfosiuf894y98s";
    let sk = ed25519_zebra::SigningKey::new(rand::thread_rng());

    let now = std::time::Instant::now();
    let sig = sk.sign(msg);
    println!("{:?}", sig);
    let elapsed = now.elapsed();
    println!("Elapsed: {:.2?}", elapsed);

    let vk = ed25519_zebra::VerificationKey::from(&sk);
    let now = std::time::Instant::now();
    vk.verify(&sig, msg).unwrap();
    let elapsed = now.elapsed();
    println!("Elapsed: {:.2?}", elapsed);
}

@bob333
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bob333 commented Sep 15, 2022

What is "Zippy"? Is it a google internal compression software?

@Yrwein
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Yrwein commented Oct 4, 2022

@milesrichardson
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Send 1K bytes over 1 Gbps network 10,000 ns 10 us

this seems misleading, since in common networking terminology 1 Gbps refers to throughput ("size of the pipe"), but this list is about "latency," which is generally independent of throughput - it takes the same amount of time to send 1K bytes over a 1 Mbps network and a 1 Gbps network

A better description of this measure sounds like "bit rate," or more specifically the "data signaling rate" (DSR) over some communications medium (like fiber). This also avoids the ambiguity of "over" the network (how much distance?) because DSR measures "aggregate rate at which data passes a point" instead of a segment.

Using this definition (which I just learned a minute ago), perhaps a better label would be:

- Send 1K bytes over 1 Gbps network       10,000   ns       10 us
+ Transfer 1K bytes over a point on a 1 Gbps fiber channel       10,000   ns       10 us

🤷 (also, I didn't check if the math is consistent with this labeling, but I did pull "fiber channel" from the table on the DSR wiki page)

@nking
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nking commented Jun 8, 2023

Thanks for sharing your updates.

You could consider adding a context switch for threads, right under disk seek in your table:
computer context switches as writing to memory ~ 100 ns

@VTrngNghia
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I see "Read 1 MB sequentially from disk", but how about disk write?

@SergeSEA
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SergeSEA commented Dec 20, 2023

the numbers are from Dr. Dean from Google reveals the length of typical computer operations in 2010. I hope someone could update them as it's 2023

@VTrngNghia
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The numbers should be still quite similar.

These numbers based on Physical limitation only significant technological leap can make a difference.

In any case, these are for estimates, not exact calculation. For example, 1MB read from SSD is different for each SSD, but it should be somewhere around the Millisecond range.

@xealits
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xealits commented Jan 31, 2024

it could be useful to add a column with the sizes in the hierarchy. Also, a column of the minimal memory units sizes, the cache line sizes etc. Then you can also divide the sizes by the latencies, which would be some kind of limit for a simple algorithm throughput. Not really sure if this is useful though.

@robertknight
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As an updated point of reference for the first few numbers, Apple give a table in their Apple Silicon CPU Optimization guide. You can see they are extremely similar to the original figures:

Apple Silicon CPU latency

@hernaneg350
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hernaneg350 commented Oct 12, 2024

Just a note for whomever wants to use this as a reference: I personally understand this does not take queuing & contention into account.

Numbers should change when physical devices have contention (CPU, Memory buffers, NIO, Thread pools) so things might be slightly larger in the average case (usually you'd try to maximize utilization and tradeoff for some contention) and quite larger on worst case (when that optimization goes wrong or you botched the design with bad bottlenecks).

This is amazing work btw and I'm glad to see how the community has added specs, references and notes on top of it.

@jboner
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Author

jboner commented Oct 17, 2024

Thanks for the comments and suggestions. This is not my original work; it's a community effort.

@josephjoeljo
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One more thing I gotta memorize 😔

@vbansal2
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vbansal2 commented Oct 25, 2024

Let's use 🍌 for the scale 👉

Operation Time (ns) Banana Units
L1 cache reference 0.5 ns 1 banana (one banana)
Branch mispredict 5 ns 10 bananas (ten bananas)
L2 cache reference 7 ns 14 bananas (fourteen bananas)
Mutex lock/unlock 25 ns 50 bananas (fifty bananas)
Main memory reference 100 ns 200 bananas (two hundred bananas)
Compress 1K bytes with Zippy 3,000 ns 6,000 bananas (six thousand bananas)
Send 1K bytes over 1 Gbps network 10,000 ns 20,000 bananas (twenty thousand bananas)
Read 4K randomly from SSD 150,000 ns 300,000 bananas (three hundred thousand bananas)
Read 1 MB sequentially from memory 250,000 ns 500,000 bananas (five hundred thousand bananas)
Round trip within same datacenter 500,000 ns 1,000,000 bananas (one million bananas)
Read 1 MB sequentially from SSD 1,000,000 ns 2,000,000 bananas (two million bananas)
Disk seek 10,000,000 ns 20,000,000 bananas (twenty million bananas)
Read 1 MB sequentially from disk 20,000,000 ns 40,000,000 bananas (forty million bananas)
Send packet CA->Netherlands->CA 150,000,000 ns 300,000,000 bananas (three hundred million bananas)

In this table, each operation's latency is expressed in terms of the smallest unit—a single L1 cache reference, which is equivalent to 1 banana.

@speculatrix
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while I find the idea of a banana as a base unit of distance, it's not really helpful here. however, you could do a scale of distances, starting at the planck length in femto bananas or something.

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