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Memtest86 v8.4 free - no SMT support on a Ryzen machine

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  • Memtest86 v8.4 free - no SMT support on a Ryzen machine

    I am using Memtest v8.4 free with a Ryzen 5 3600 6-core CPU system.
    During some previuos test a year ago or so it used to use SMT (i.e. run tests on 12 threads) by default.
    Now, the same exact image on the same exact flash drive does not use SMT (6 CPUS working, 6 CPUs disabled). Thus, it is not the case on the hyperthreads not being used by default in the newer versions of Memtest86.

    I've tested the flash drive on a different Ryzen system, also 6 core/12 thread, and got 12 CPUs running with Memtest86 by default.

    On the machine of interest, SMT is enabled, other CPU settings are auto, in linux 12 threads are active, and yet Memtest only uses physical cores - on that specific machine. The machine exhibited some suspicious behaviour, but the memory tests are clean. The only weird part is Memtest's CPU selection.
    ​I wonder if this indicates some problem with the CPU. Any ideas?

    ​Please delete the previous (shorter) post. Thank you.

  • #2
    MemTest86 release history

    Version 7.3 - 27/Feb/2017
    • ​CPU cores that are identified as hyperthreads are now disabled by default, due to minimal performance benefits
    • Added 'ENABLEHT' config file parameter to enable/disable CPU cores identified as hyperthreads​
    In fact, we found memory testing was slower with Hyperthreads enabled on some systems. You can force them on from the Config file however.


    • #3
      Thank you for the answer.
      I am concerned with something else though. v8.4, the same flash drive, the same image, behaves differently on two different Ryzen machines, both 6 cores and 12 threads, SMT (HT) enabled in BIOS. On one of them, 12 CPUs are active during the tests (Memtest64 uses SMT), while on the other one 6 are active and 6 are disabled (Memtest64 does not use SMT.
      Does that solely depend on the BIOS setting and CPU detection, or can something be wrong with one of the CPUs? I'd expect the same behavoiur on both.

      I am interested in memory testing under high multithread load, hence the question.


      • #4
        We no longer support V8. So can you check the V10 behavior?