markdown 每个程序员都应该知道的延迟数

Posted 2021-05-06

| Task                               |          ns |      us |  ms |                               |
|:-----------------------------------|------------:|--------:|----:|------------------------------:|
| L1 cache reference                 |         0.5 |         |     |                               |
| Branch mispredict                  |           5 |         |     |                               |
| L2 cache reference                 |           7 |         |     |  14x L1 cache                 |
| Mutex lock/unlock                  |          25 |         |     |                               |
| Main memory reference              |         100 |         |     |  20x L2 cache, 200x L1 cache  |
| Compress 1K bytes with Zippy       |       3,000 |       3 |     |                               |
| Send 1K bytes over 1 Gbps network  |      10,000 |      10 |     |                               |
| Read 4K randomly from SSD*         |     150,000 |     150 |     | ~1GB/sec SSD                  |
| Read 1 MB sequentially from memory |     250,000 |     250 |     |                               |
| Round trip within same datacenter  |     500,000 |     500 |     |                               |
| Read 1 MB sequentially from SSD*   |   1,000,000 |   1,000 |   1 | ~1GB/sec SSD, 4X memory       |
| Disk seek                          |  10,000,000 |  10,000 |  10 | 20x datacenter roundtrip      |
| Read 1 MB sequentially from disk   |  20,000,000 |  20,000 |  20 | 80x memory, 20X SSD           |
| Send packet<br>CA->Netherlands->CA | 150,000,000 | 150,000 | 150 |                               |

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