linux-kernel - RE: [RFC] x86, tsc: Add kcmdline args for skipping tsc calibration sequences

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Date:   Sat, 14 Jul 2018 02:40:48 +0000
From:   "Brown, Len" <len.brown@...el.com>
To:     patrickg <patrickg@...ermicro.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "mingo@...nel.org" <mingo@...nel.org>,
        "Du, Alek" <alek.du@...el.com>,
        "arjan@...ux.intel.com" <arjan@...ux.intel.com>,
        "Tang, Feng" <feng.tang@...el.com>
Subject: RE: [RFC] x86, tsc: Add kcmdline args for skipping tsc calibration
 sequences

We disabled CPUID-based TSC calibration on SKX in December for several reasons.
If you still have it enabled, you need this patch:

commit b511203093489eb1829cb4de86e8214752205ac6
    x86/tsc: Fix erroneous TSC rate on Skylake Xeon

If you are referring to another platform that has CPUID-TSC calibration...
it should still work on an over-clocked system.  Over-clocked platforms should
use exactly the same reference crystal as non-overclocked platforms, but should
modify the crystal/core multiplier.   If you are changing the reference
crystal, then I believe you are using an un-supported hardware configuration,
and my ability to support you is limited.

-Len