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FSGSBASE Testing Is Encouraged Ahead Of Linux 5.9

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  • Space Heater
    replied
    Originally posted by damentz View Post
    FSGSBASE patches seem to have issues with host systems running VMs through VirtualBox on Ryzen processors. I had to remove FSGSBASE patches from Zen Kernel after a report that a 3950x user was getting stalls and freezes after the patches were added: https://github.com/zen-kernel/zen-kernel/issues/172
    I saw in the bug report another user reported system freezes with qemu/kvm virtual machines and FSGSBASE.

    On 5.8-rc2 with FSGSBASE patches, I've run a Windows vm via qemu/kvm for over 12 hours now and so far I've experienced no hangs or oops messages.

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  • V1tol
    replied
    Another one stupid question - if I use "mitigations=off" will performance change at all with this patch?

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  • ezst036
    replied
    Thank you.

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  • Space Heater
    replied
    Originally posted by ezst036 View Post
    what would be the earliest processor family that might benefit from this?
    It would appear that 15h and newer support FSGSBASE, so that is Bulldozer and newer. I'm not sure if 16h (Jaguar/Puma) support it though.

    Source: AMD's BIOS and Kernel Developer’s Guide. (page 32, under "Architectural changes")

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  • ezst036
    replied
    Originally posted by Beherit View Post
    Is it true this also speeds up AMD CPUs?
    For anybody who knows, what would be the earliest processor family that might benefit from this? Bulldozer? K10h?(phenom II, etc)

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  • Space Heater
    replied
    Originally posted by damentz View Post
    FSGSBASE patches seem to have issues with host systems running VMs through VirtualBox on Ryzen processors.
    Given that the bug report was posted before the current revision of the FSGSBASE patches came out, I'd suggest checking again to see if the problem still persists (and on an otherwise mainline kernel).

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  • damentz
    replied
    FSGSBASE patches seem to have issues with host systems running VMs through VirtualBox on Ryzen processors. I had to remove FSGSBASE patches from Zen Kernel after a report that a 3950x user was getting stalls and freezes after the patches were added: https://github.com/zen-kernel/zen-kernel/issues/172

    Leave a comment:


  • _Alex_
    replied
    In the geometric mean, AMD got more performance (+7.3% vs intel 6.1%): https://openbenchmarking.org/embed.p...ha=432aff7&p=2

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  • Space Heater
    replied
    Originally posted by Beherit View Post
    Is it true this also speeds up AMD CPUs?
    Yes, but the improvement isn't likely to be as noticeable, as context switches are currently less expensive on AMD systems.

    You can look at Michael's earlier benchmarks.

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  • milkylainen
    replied
    Just the sheer engineering keeping the old turd afloat...

    I remember when cpuinfo features was a oneliner. Now it's like a novel...
    ... And f00f/fdiv was all you needed to know before Intel screwed everything up...
    Last edited by milkylainen; 06-21-2020, 03:22 AM.

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