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After 5 Years, FSGSBASE Support Finally Ready For Linux To Enhance AMD/Intel Performance

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  • After 5 Years, FSGSBASE Support Finally Ready For Linux To Enhance AMD/Intel Performance

    Phoronix: After 5 Years, FSGSBASE Support Finally Ready For Linux To Enhance AMD/Intel Performance

    The Linux kernel work for making use of the x86_64 FSGSBASE instruction since Intel Ivy Bridge and since then AMD CPUs also is set to finally land with the in-development Linux 5.9 kernel. The FSGSBASE support has the possibility of helping Intel/AMD CPU performance especially in areas like context switching that had been hurt badly by Spectre/Meltdown and other CPU vulnerability mitigations largely on the Intel side...

    http://www.phoronix.com/scan.php?pag...-For-Linux-5.9

  • #2
    Why was it dropped by intel in the first place? It looks like this patch is at least cleaning up a bit of the Spectre performance penalty mess. This is even in their PR interests. ...yeah we scrwed it but we have figured out a way to compensate a bit of it.

    Just speculating ...do they fear an old CPU without hardware mitigation plus this patch will outperform a new CPU with hardware mitigation + this patch?
    Last edited by CochainComplex; 08-04-2020, 09:56 AM.

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    • #3
      Would love to see this compared with and without mitigations - i.e. does it speed things up even when mitigations=off is set

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      • #4
        What about preliminary Glibc HWCAPS bencmarks for Zen, Zen (called Zen1.5 by myself) and Zen2
        https://www.phoronix.com/scan.php?pa...ibc-hwcaps-RFC
        ?
        And what about use of similar technologies inside kernel out of arch directory (inside menuconfig rule of kernel makefile is so obsolete)

        Maybe some multi-architecture kernel build is to be mentioned. (use of NOP to ensure same virtual address for more architectures and for example use two pagetabeles - one for x86_64, one for ARMv8a for example and after switch to other CPU just set correct table to CR3 for x86 or similar register for ARM)


        Maybe soft of "Skybridge 2" (Skybridge with multiple architecture chiplets inside same CPU package)
        https://www.electronicdesign.com/tec...-and-64bit-arm
        may be possible then

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        • #5
          Originally posted by FireBurn View Post
          Would love to see this compared with and without mitigations - i.e. does it speed things up even when mitigations=off is set
          Here are some numbers from last year compared to unmitigated - https://www.phoronix.com/scan.php?pa...fsgsbase&num=2
          Michael Larabel
          http://www.michaellarabel.com/

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          • #6
            Originally posted by FireBurn View Post
            Would love to see this compared with and without mitigations - i.e. does it speed things up even when mitigations=off is set
            https://github.com/xanmod/linux it has the FSGSBASE patch.

            use the mitigation=off kernel boot parameter
            Last edited by CochainComplex; 08-04-2020, 10:39 AM.

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            • #7
              Excellent improvement!

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              • #8
                Originally posted by Michael View Post

                Here are some numbers from last year compared to unmitigated - https://www.phoronix.com/scan.php?pa...fsgsbase&num=2
                This is not comparing perf of FSGBASE with AND without mitigations as FireBurn asked. I would be interested in tat too.

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                • #9
                  after Intel dropped the ball
                  this is intel for you they dropped support like intel stock drop every years

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                  • #10
                    Well, if you want to get more performance out of your system, go ahead and install the Xanmod kernel. It has enabled FSGSBASE in stable 5.7 and in 5.8 edge.
                    No problems found when using it in Ubuntu.

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