Latency Numbers Every Programmer Should Know - MarkDown Fork

latency_numbers.md

Latency Comparison Numbers

Note: "Forked" from Latency Numbers Every Programmer Should Know

Event	Nanoseconds	Microseconds	Milliseconds	Comparison
L1 cache reference	0.5	-	-	-
Branch mispredict	5.0	-	-	-
L2 cache reference	7.0	-	-	14x L1 cache
Mutex lock/unlock	25.0	-	-	-
Main memory reference	100.0	-	-	20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy	3,000.0	3	-	-
Send 1K bytes over 1 Gbps network	10,000.0	10	-	-
Read 4K randomly from SSD	150,000.0	150	-	~1GB/sec SSD
Read 1 MB sequentially from memory	250,000.0	250	-	-
Round trip within same datacenter	500,000.0	500	-	-
Read 1 MB sequentially from SSD	1,000,000.0	1,000	1	~1GB/sec SSD, 4X memory
Disk seek	10,000,000.0	10,000	10	20x datacenter roundtrip
Read 1 MB sequentially from disk	20,000,000.0	20,000	20	80x memory, 20X SSD
Send packet CA → Netherlands → CA	150,000,000.0	150,000	150	-

Unit Reference

• 1 ns = 10^-9 seconds
• 1 µs = 10^-6 seconds = 1,000 ns
• 1 ms = 10^-3 seconds = 1,000 µs = 1,000,000 ns

Credit/Notes

• By Jeff Dean
• Originally by Peter Norvig
• Presentation - Latency Numbers for Programmers

Visual Comparison Charts

The numbers for main memory reference don't add up. They are 100x L1, but only 14.28x the L2 numbers given, not the 20x stated.

How long will it take to read 1kb from SSD? (Definitely not 1/1024 of time you need to read 1Mb, right?)