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Looking At The Linux Performance Two Years After Spectre / Meltdown Mitigations

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  • #31
    Originally posted by F.Ultra View Post

    HW is not magic, if you have to clear a certain cache in a particular way to avoid the mitigation it does not matter much if that clear cmd is done in the cpu microcode or if it's done in SW. Yes it could be done slightly faster in some cases in HW but one advantage that SW have over HW is that the SW can choose when and where to apply the mitigation while the HW have to apply it everywhere so we can e.g implement certain things only where it matters (inside the kernel) and ignore it in say userspace where it does not matter (depends upon the mitigation of course).

    A new architecture that is built from scratch to avoid this family of vulnerabilities will take several years to develop and even then it's very likely that those CPUs will be slower than todays CPUs clock for clock (and thus perhaps never even released). There might just not be any way that you can perform speculative execution safely and if you completely disable that performance will go down the drain.
    Wow. This is a great explanation.
    Yes, if in fact cache has to be cleared, that means a huge impact on performance.
    Makes sense.

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    • #32
      Originally posted by nomadewolf View Post

      Couldn't Intel be just doing software mitigations via firmware on the new chips?
      yeah, I'm sure they must be

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      • #33
        Glad to see that it's not entirely a dumpster fire for Intel (especially servers). Still, the fact that this happened and was known for nearly a decade really sours me on Intel. New devices I am buying will have AMD or ARM CPUs in them. I know AMD is affected to some degree, I'm not sure if ARM-based chips were hit. Hopefully this issue was a shot across the bow of future manufacturers.

        Probably not, though. We'll get the same trash with a different package and a promise that things are all better now (read: different problem, same scale).

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        • #34
          Originally posted by ndegruchy View Post
          I know AMD is affected to some degree, I'm not sure if ARM-based chips were hit.
          out-of-order ARM chips (A72, A75, A76, etc) were hit about the same as AMD. in-order ones (A53, A55, etc) aren't affected, but are obviously much slower. right now the best way to go looks like ARM for low power stuff and AMD for everything else.

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