• Rasmus Villemoes's avatar
    powerpc/fadump: rename cpu_online_mask member of struct fadump_crash_info_header · a0512164
    Rasmus Villemoes authored
    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 nowadays [1] 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
    4/6).
    
    Patch 1/6 is new in v2, and fixes a build failure on ppc by renaming a
    struct member, to avoid problems when the identifier cpu_online_mask
    becomes a macro later in the series.  The next 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 on x86_64, bloat-o-meter says we save ~3000 bytes.
    We also save a little stack (stackdelta says 127 functions have a 16 byte
    smaller stack frame, while two grow by that amount).  Mostly because, when
    iterating over the mask, gcc typically loads the value of cpu_xyz_mask
    into a callee-saved register and from there into %rdi before each
    find_next_bit call - now it can just load the appropriate immediate
    address into %rdi before each call.
    
    [1] See Rusty's kind explanation
    http://thread.gmane.org/gmane.linux.kernel/2047078/focus=2047722 for
    some historic context.
    
    This patch (of 6):
    
    As preparation for eliminating the indirect access to the various global
    cpu_*_bits bitmaps via the pointer variables cpu_*_mask, rename the
    cpu_online_mask member of struct fadump_crash_info_header to simply
    online_mask, thus allowing cpu_online_mask to become a macro.
    Signed-off-by: default avatarRasmus Villemoes <linux@rasmusvillemoes.dk>
    Acked-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Rusty Russell <rusty@rustcorp.com.au>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    a0512164
fadump.h 5.96 KB