linux-kernel - [PATCH 0/4] x86/platform/UV: Update TSC support

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Date:   Thu, 28 Sep 2017 13:03:39 -0500
From:   <mike.travis@....com>
To:     Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Bin Gao <bin.gao@...ux.intel.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Andrew Banman <andrew.banman@....com>,
        Russ Anderson <russ.anderson@....com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: [PATCH 0/4] x86/platform/UV: Update TSC support


The UV BIOS goes to considerable effort to get the TSC synchronization
accurate across the entire system.  Included in that are multiple chassis
that can have 32+ sockets.  The architecture does support an external
high resolution clock to aid in maintaining this synchronization.

The resulting TSC accuracy set by the UV system BIOS is much better
than the generic kernel TSC ADJUST functions.  This is important for
applications that read the TSC values directly for accessing data bases.

*   These patches disable an assumption made by the kernel tsc sync
    functions that Socket 0 in the system should have a TSC ADJUST
    value of zero.  This is not correct when the chassis are reset
    asynchronously to each other so which TSC's should be zero is
    not predictable.

*   When the system BIOS determines that the TSC is not stable, it then
    sets a flag so the UV kernel setup can set the "tsc is unstable"
    flag.  A patch now prevents the kernel from attempting to fix the
    TSC causing a slew of warning messages.

*   It also eliminates another avalanche of warning messages from older
    BIOS that did not have the TSC ADJUST MSR (ex. >3000 msgs in a 32
    socket Skylake system).  It now notes this with a single warning
    message and then moves on with fixing them.

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