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When adding gettime64() to a 32 bit architecture (namely powerpc/32) it has been noticed that GCC doesn't inline anymore __cvdso_clock_gettime_common() because it is called twice (Once by __cvdso_clock_gettime() and once by __cvdso_clock_gettime32). This has the effect of seriously degrading the performance: Before the implementation of gettime64(), gettime() runs in: clock-gettime-monotonic-raw: vdso: 1003 nsec/call clock-gettime-monotonic-coarse: vdso: 592 nsec/call clock-gettime-monotonic: vdso: 942 nsec/call When adding a gettime64() entry point, the standard gettime() performance is degraded by 30% to 50%: clock-gettime-monotonic-raw: vdso: 1300 nsec/call clock-gettime-monotonic-coarse: vdso: 900 nsec/call clock-gettime-monotonic: vdso: 1232 nsec/call Adding __always_inline() to __cvdso_clock_gettime_common() regains the original performance. In terms of code size, the inlining increases the code size by only 176 bytes. This is in the noise for a kernel image. Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/1ab6a62c356c3bec35d1623563ef9c636205bcda.1588079622.git.christophe.leroy@c-s.fr
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.