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Local register variables were used in an effort to improve the accuracy of the measurement of cache residency of a pseudo-locked region. This was done to ensure that only the cache residency of the memory is measured and not the cache residency of the variables used to perform the measurement. While local register variables do accomplish the goal they do require significant care since different architectures have different registers available. Local register variables also cannot be used with valuable developer tools like KASAN. Significant testing has shown that similar accuracy in measurement results can be obtained by replacing local register variables with regular local variables. Make use of local variables in the critical code but do so with READ_ONCE() to prevent the compiler from merging or refetching reads. Ensure these variables are initialized before the measurement starts, and ensure it is only the local variables that are accessed during the measurement. With the removal of the local register variables and using READ_ONCE() there is no longer a motivation for using a direct wrmsr call (that avoids the additional tracing code that may clobber the local register variables). Signed-off-by: Reinette Chatre <reinette.chatre@intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: fenghua.yu@intel.com Cc: tony.luck@intel.com Cc: acme@kernel.org Cc: gavin.hindman@intel.com Cc: jithu.joseph@intel.com Cc: dave.hansen@intel.com Cc: hpa@zytor.com Link: https://lkml.kernel.org/r/f430f57347414e0691765d92b144758ab93d8407.1537377064.git.reinette.chatre@intel.com
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.