mirror of
https://github.com/hardkernel/linux.git
synced 2026-06-09 12:17:12 +09:00
a7ec817d55
The kernel assumes that the TSC frequency which is provided by the hardware / firmware via MSRs or CPUID(0x15) is correct after applying a few basic consistency checks. This disables the TSC recalibration against HPET or PM timer. As a result there is no mechanism to validate that frequency in cases where a firmware or hardware defect is suspected. And there was case that some user used atomic clock to measure the TSC frequency and reported an inaccuracy issue, which was later fixed in firmware. Add an option 'recalibrate' for 'tsc' kernel parameter to force the tsc freq recalibration with HPET or PM timer, and warn if the deviation from previous value is more than about 500 PPM, which provides a way to verify the data from hardware / firmware. There is no functional change to existing work flow. Recently there was a real-world case: "The 40ms/s divergence between TSC and HPET was observed on hardware that is quite recent" [1], on that platform the TSC frequence 1896 MHz was got from CPUID(0x15), and the force-reclibration with HPET/PMTIMER both calibrated out value of 1975 MHz, which also matched with check from software 'chronyd', indicating it's a problem of BIOS or firmware. [Thanks tglx for helping improving the commit log] [ paulmck: Wordsmith Kconfig help text. ] [1]. https://lore.kernel.org/lkml/20221117230910.GI4001@paulmck-ThinkPad-P17-Gen-1/ Signed-off-by: Feng Tang <feng.tang@intel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: <x86@kernel.org> Cc: <linux-doc@vger.kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.