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C0.2 state in umwait and tpause instructions can be enabled or disabled on a processor through IA32_UMWAIT_CONTROL MSR register. By default, C0.2 is enabled and the user wait instructions results in lower power consumption with slower wakeup time. But in real time systems which require faster wakeup time although power savings could be smaller, the administrator needs to disable C0.2 and all umwait invocations from user applications use C0.1. Create a sysfs interface which allows the administrator to control C0.2 state during run time. Andy Lutomirski suggested to turn off local irqs before writing the MSR to ensure the cached control value is not changed by a concurrent sysfs write from a different CPU via IPI. [ tglx: Simplified the update logic in the write function and got rid of all the convoluted type casts. Added a shared update function and made the namespace consistent. Moved the sysfs create invocation. Massaged changelog ] Signed-off-by: Fenghua Yu <fenghua.yu@intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Ashok Raj <ashok.raj@intel.com> Reviewed-by: Tony Luck <tony.luck@intel.com> Cc: "Borislav Petkov" <bp@alien8.de> Cc: "H Peter Anvin" <hpa@zytor.com> Cc: "Andy Lutomirski" <luto@kernel.org> Cc: "Peter Zijlstra" <peterz@infradead.org> Cc: "Ravi V Shankar" <ravi.v.shankar@intel.com> Link: https://lkml.kernel.org/r/1560994438-235698-4-git-send-email-fenghua.yu@intel.com |
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| kernel | ||
| lib | ||
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| .clang-format | ||
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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.