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458ef2a25e
- A series of commits to make the MSR derived CPU and TSC frequency more
accurate.
It turned out that the frequency tables which have been taken from the
SDM are inaccurate because the SDM provides truncated and rounded
values, e.g. 83.3Mhz (83.3333...) or 116.7Mhz (116.6666...).
This causes time drift in the range of ~1 second per hour
(20-30 seconds per day). On some of these SoCs it's not possible to
recalibrate the TSC because there is no reference (PIT, HPET) available.
With some reverse engineering it was established that the possible
frequencies are derived from the base clock with fixed multiplier /
divider pairs.
For the CPU models which have a known crystal frequency the kernel now
uses multiplier / divider pairs which bring the frequencies closer to
reality and fix the observed time drift issues.
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Merge tag 'x86-timers-2020-03-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 timer updates from Thomas Gleixner:
"A series of commits to make the MSR derived CPU and TSC frequency more
accurate.
It turned out that the frequency tables which have been taken from the
SDM are inaccurate because the SDM provides truncated and rounded
values, e.g. 83.3Mhz (83.3333...) or 116.7Mhz (116.6666...).
This causes time drift in the range of ~1 second per hour (20-30
seconds per day). On some of these SoCs it's not possible to
recalibrate the TSC because there is no reference (PIT, HPET)
available.
With some reverse engineering it was established that the possible
frequencies are derived from the base clock with fixed multiplier /
divider pairs.
For the CPU models which have a known crystal frequency the kernel now
uses multiplier / divider pairs which bring the frequencies closer to
reality and fix the observed time drift issues"
* tag 'x86-timers-2020-03-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/tsc_msr: Make MSR derived TSC frequency more accurate
x86/tsc_msr: Fix MSR_FSB_FREQ mask for Cherry Trail devices
x86/tsc_msr: Use named struct initializers
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| README | ||
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.