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99c19e6a8f
vgetcyc() is full of barriers, so fetching values out of the vvar page before vgetcyc() for use after vgetcyc() results in poor code generation. Put vgetcyc() first to avoid this problem. Also, pull the tv_sec division into the loop and put all the ts writes together. The old code wrote ts->tv_sec on each iteration before the syscall fallback check and then added in the offset afterwards, which forced the compiler to pointlessly copy base->sec to ts->tv_sec on each iteration. The new version seems to generate sensible code. Saves several cycles. With this patch applied, the result is faster than before the clock_gettime() rewrite. Signed-off-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/3c05644d010b72216aa286a6d20b5078d5fae5cd.1538762487.git.luto@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.
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.