[lkml]   [2015]   [Sep]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Subject[PATCH 0/5] kernel/cpu.c: eliminate some indirection
Maybe third time's the charm...

The four cpumasks cpu_{possible,online,present,active}_bits are
exposed readonly via the corresponding const variables
cpu_xyz_mask. But they are also accessible for arbitrary writing via
the exposed functions set_cpu_xyz. There's quite a bit of code
throughout the kernel which iterates over or otherwise accesses these
bitmaps, and having the access go via the cpu_xyz_mask variables is
simply a useless indirection.

It may be that any problem in CS can be solved by an extra level of
indirection, but that doesn't mean every extra indirection solves a
problem. In this case, it even necessitates some minor ugliness (see

The first four patches eliminate the cpu_xyz_mask variables by simply
exposing the actual bitmaps, after renaming them to discourage direct
access - that still happens through cpu_xyz_mask, which are now simply
macros with the same type and value as they used to have.

After that, there's no longer any reason to have the setter functions
be out-of-line: The boolean parameter is almost always a literal true
or false, so by making them static inlines they will usually compile
to one or two instructions.

For a defconfig build, bloat-o-meter says we save ~3000 bytes.

Rasmus Villemoes (5):
kernel/cpu.c: change type of cpu_possible_bits and friends
kernel/cpu.c: export __cpu_*_mask
drivers/base/cpu.c: use __cpu_*_mask directly
kernel/cpu.c: eliminate cpu_*_mask
kernel/cpu.c: make set_cpu_* static inlines

drivers/base/cpu.c | 10 ++++----
include/linux/cpumask.h | 55 +++++++++++++++++++++++++++++++++++-------
kernel/cpu.c | 64 ++++++++++---------------------------------------
3 files changed, 65 insertions(+), 64 deletions(-)


 \ /
  Last update: 2015-09-25 20:41    [W:0.070 / U:9.084 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site