4 ms·

How are you defining memory performance and where are your supporting comparisons? This article only discusses the M1's behavior, and makes no comparisons to an

How are you defining memory performance and where are your supporting comparisons? This article only discusses the M1's behavior, and makes no comparisons to any other CPU.

FabHK 6y ago
FWIW, I ran it on a MacBook Pro (13-inch, 2019, Four Thunderbolt 3 ports), 2.4 GHz Quad-Core Intel Core i5, 8 GB 2133 MHz LPDDR3: two : 49.6 ns (x 5.5) two+ : 64.8 ns (x 5.2) three: 72.8 ns (x 5.6) EDIT to add: above was just `cc`. Below is with `cc -O3 -Wall`, as in Lemire's article: two : 62.8 ns (x 7.1) two+ : 69.2 ns (x 5.5) three: 95.3 ns (x 7.3)
- namibj 6y ago
  You _need_ to use -mnative because it otherwise retains backwards compatibility to older x86.
  - FabHK 6y ago
    (base) Coding % cc -mnative two-three.c clang: error: unknown argument: '-mnative' (base) Coding % cc -v Apple clang version 12.0.0 (clang-1200.0.32.28) Target: x86_64-apple-darwin20.2.0 Thread model: posix
    - astrange 6y ago
      It's spelled "-march=native" in gcc and "-arch x86_64h" in clang. It doesn't make much difference though, autovectorization doesn't work very well and there is not a lot of special optimization for newer x86 CPUs.
      - namibj 6y ago
        All recent Intel Core-i microarchitectures require using full vector width loads to max out L1d bandwidth, because the load/store units don't actually care about the width of a load, as long as it doesn't cross a cache line (in which case the typical penalty is an additional cycle). Only using 128 bit wide instructions on a core that has 512 bit hardware results in 4x less L1d bandwidth.
- deleted 6y ago
  [deleted]
- africanboy 6y ago
  there must be something wrong there, on my late 2014 laptop that mounts Type: DDR4 Speed: 2133 MT/s I get two : 27.1 ns (3x) two+ : 28.6 ns (2.2x) three: 39.7 ns (3x) which is not much, considering this is an almost 6 years old system with 2x slower memor
  - FabHK 6y ago
    Dunno, I didn't reboot and didn't close all other programs (browser, editor, mail, calendar, notes, editor)... Top shows Load Avg: 2.36, 2.01, 1.97 CPU usage: 2.10% user, 3.39% sys, 94.49% idle

How are you defining memory performance and where are your supporting comparisons? This article only discusses the M1's behavior, and makes no comparisons to any other CPU.

FabHK 6y ago

FWIW, I ran it on a MacBook Pro (13-inch, 2019, Four Thunderbolt 3 ports), 2.4 GHz Quad-Core Intel Core i5, 8 GB 2133 MHz LPDDR3: two : 49.6 ns (x 5.5) two+ : 64.8 ns (x 5.2) three: 72.8 ns (x 5.6) EDIT to add: above was just `cc`. Below is with `cc -O3 -Wall`, as in Lemire's article: two : 62.8 ns (x 7.1) two+ : 69.2 ns (x 5.5) three: 95.3 ns (x 7.3)

namibj 6y ago
You _need_ to use -mnative because it otherwise retains backwards compatibility to older x86.
- FabHK 6y ago
  (base) Coding % cc -mnative two-three.c clang: error: unknown argument: '-mnative' (base) Coding % cc -v Apple clang version 12.0.0 (clang-1200.0.32.28) Target: x86_64-apple-darwin20.2.0 Thread model: posix
  - astrange 6y ago
    It's spelled "-march=native" in gcc and "-arch x86_64h" in clang. It doesn't make much difference though, autovectorization doesn't work very well and there is not a lot of special optimization for newer x86 CPUs.
    - namibj 6y ago
      All recent Intel Core-i microarchitectures require using full vector width loads to max out L1d bandwidth, because the load/store units don't actually care about the width of a load, as long as it doesn't cross a cache line (in which case the typical penalty is an additional cycle). Only using 128 bit wide instructions on a core that has 512 bit hardware results in 4x less L1d bandwidth.
deleted 6y ago
[deleted]
africanboy 6y ago
there must be something wrong there, on my late 2014 laptop that mounts Type: DDR4 Speed: 2133 MT/s I get two : 27.1 ns (3x) two+ : 28.6 ns (2.2x) three: 39.7 ns (3x) which is not much, considering this is an almost 6 years old system with 2x slower memor
- FabHK 6y ago
  Dunno, I didn't reboot and didn't close all other programs (browser, editor, mail, calendar, notes, editor)... Top shows Load Avg: 2.36, 2.01, 1.97 CPU usage: 2.10% user, 3.39% sys, 94.49% idle