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Fresh Linux 4.16 Kernel Benchmarks With KPTI & Retpolines

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  • #21
    'The Linux kernel build time fortunately was not impacted on this high-end Intel Xeon Scalable server.'

    _My_ real kernel compiles (amd-staging-drm-next) went down from ~7:30 min to 8:30 min ;-(
    running 4.15-rc amd-staging-drm-next (without any mitigation) before
    now 4.16.0-rc1 amd-staging-drm-next (all mitigation)
    on X3470, 4C/8T, 2,93 GHz, 24 GB Nehalem (sadly without PCID)

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    • #22
      Is it only Kernel or Kernel + Firmware?
      For instance, if I have Linux Mint and I want to get back to the state before any "Mitigation" applied.
      What should I do?

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      • #23
        For Nehalem (Lynnfield, Xeon versions) new firmware is currently only 'planned'.
        Last edited by nuetzel; 03-08-2018, 03:56 AM. Reason: typo

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        • #24
          I'm new to the Linux Eco System.
          What I mean is on Linux Mint 18.3 when the "Anti Spctre & Meltdown" updates were out the system asked to update 2 things:
          1. Linux Kernel.
          2. Linux Firmware.

          What I ask is how can I roll it back to the latest Kernel + Firmware before those performance killer updates?

          Thank You.

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          • #25
            Ah, sorry.
            For latest 4.15.x and above (backported, too) you should append

            nopti, nospectre_v2 --- nospectre_v1 (isn't ready, documented, yet - but you can try it)

            Linux kernel source tree <Documentation/admin-guide/kernel-parameters.txt>

            New firmware should be NO problem.

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            • #26
              Do you mean compiling it by myself?
              Can't I just manually install versions prior to the fix?

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              • #27
                Originally posted by Royi View Post
                Do you mean compiling it by myself?
                You _can_ do that, but... - NO, not needed.

                You 'only' have to append the above _kernel boot_ parameter (grep for 'grub' boot parameter for example or your distro's boot loader), to disable the mitigation.

                Can't I just manually install versions prior to the fix?
                This is possible, too. - But why would you lose all other new kernel stuff (see above)?

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                • #28
                  nuetzel , Since I didn't understand what you meant (I'm new to the Linux world).
                  Could you explain it again?

                  Thank You.

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                  • #29
                    Originally posted by Royi View Post
                    nuetzel , Since I didn't understand what you meant (I'm new to the Linux world).
                    Could you explain it again?

                    Thank You.
                    Start with reading Michel's latest review:
                    An Early Look At The Linux 4.16 Kernel Performance With AMD EPYC
                    https://www.phoronix.com/scan.php?pa...416-epyc&num=1

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                    • #30
                      Originally posted by Royi View Post
                      nuetzel , Since I didn't understand what you meant (I'm new to the Linux world).
                      Could you explain it again?

                      Thank You.
                      Take a look here: https://wiki.archlinux.org/index.php/Kernel_parameters

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