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As discussed in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97445 the const_ilog2 macro generates a lot of code which interferes badly with GCC inlining heuristics, until it can be proven that the ilog2 argument can or can't be simplified into a constant. It can be expressed using __builtin_clzll builtin which is supported by GCC 3.4 and later and when used only in the __builtin_constant_p guarded code it ought to always fold back to a constant. Other compilers support the same builtin for many years too. Other option would be to change the const_ilog2 macro, though as the description says it is meant to be used also in C constant expressions, and while GCC will fold it to constant with constant argument even in those, perhaps it is better to avoid using extensions in that case. [akpm@linux-foundation.org: coding style fixes] Link: https://lkml.kernel.org/r/20201120125154.GB3040@hirez.programming.kicks-ass.net Link: https://lkml.kernel.org/r/20201021132718.GB2176@tucnak Signed-off-by: Jakub Jelinek <jakub@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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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.