Timings & disk cache

[jj2007]

I had the rare occasion to zip a folder after a reboot, i.e. in a state when no files were in the disk cache. Here are the results for the first 4 runs of the program - the first run took 4 times as much time as the following three.

It's probably irrelevant for a Solid States Disk, though.

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**** started 18:03:30 ****
5155 ms for creating test.zip
246148  26.10.2023  18:03:36

**** started 18:03:46 ****
1300 ms for creating test.zip
246148  26.10.2023  18:03:47

**** started 18:04:05 ****
1271 ms for creating test.zip
246148  26.10.2023  18:04:06

**** started 18:04:11 ****
1258 ms for creating test.zip
246148  26.10.2023  18:04:12

**** started 18:04:19 ****
1263 ms for creating test.zip
246148  26.10.2023  18:04:20

[NoCforMe]

To fix that problem I suggest the Time Machine app.

[jj2007]

Approximate cost to access various caches and main memory?

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          0.5 ns - CPU L1 dCACHE reference
          1  ns - speed-of-light (a photon) travel a 1 ft (30.5cm) distance
          5  ns - CPU L1 iCACHE Branch mispredict
          7  ns - CPU L2  CACHE reference
          71  ns - CPU cross-QPI/NUMA best  case on XEON E5-46*
        100  ns - MUTEX lock/unlock
        100  ns - own DDR MEMORY reference
        135  ns - CPU cross-QPI/NUMA best  case on XEON E7-*
        202  ns - CPU cross-QPI/NUMA worst case on XEON E7-*
        325  ns - CPU cross-QPI/NUMA worst case on XEON E5-46*
      10,000  ns - Compress 1K bytes with Zippy PROCESS
      20,000  ns - Send 2K bytes over 1 Gbps NETWORK
    250,000  ns - Read 1 MB sequentially from MEMORY
    500,000  ns - Round trip within a same DataCenter
  10,000,000  ns - DISK seek
  10,000,000  ns - Read 1 MB sequentially from NETWORK
  30,000,000  ns - Read 1 MB sequentially from DISK
 150,000,000  ns - Send a NETWORK packet CA -> Netherlands
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13 years ago. See also, in that post, the fascinating conversations between Peter Cordes and
Lewis Kelsey - I am just a humble hobby programmer