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Linux 5.5 To Perform Late CPU Microcode Updates In Parallel

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  • Linux 5.5 To Perform Late CPU Microcode Updates In Parallel

    Phoronix: Linux 5.5 To Perform Late CPU Microcode Updates In Parallel

    Months ago we reported on vendors and cloud providers being interested in restoring parallel CPU microcode updates on Linux for helping large core count servers. With Linux 5.5 that change is coming...

  • #2
    "normal people" ūü§£


    • #3

      Microcode loading has always been done lazily.

      It had been switched to load-early only recently after the Haswell TSX fuckup in 2015. And they have switched to early loading for a reason. Because CPU's have been proved to be so fucked up to the degree that loading microcodes late have been demonstrated to be unreliable and unstable and crashy.

      Now after that date CPU's have been proved to be even more fucked up. What changed to make developers think that loading microcodes lazily will be safe now?


      • #4
        I think the argument is that early load will remain, but people who want to apply a microcode update prior to the next reboot will be able to do so without an unacceptable blip in performance. (Which is likely to be very small, bit the same servers for which this will be an issue are the ones least-tolerant of such blips.)

        Remember, if you are running a cloud, you really, really don't want to reboot because any reboot means everyone else rebooting - or at least being live-migrated onto another system. And if you load microcode while running live, you want it to work as fast as possible to avoid locking the CPU for too long.

        ‚Äč‚Äč‚Äč‚Äč‚Äč‚ÄčAlternately, perhaps they are in a situation where early load is not feasible for their configuration? Maybe they have a preset boot sequence for part of the way.
        Last edited by GreenReaper; 11-26-2019, 09:52 AM.