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    SubjectRe: [PATCH] percpu data: only iterate over possible CPUs
    Linus Torvalds <torvalds@osdl.org> wrote:
    >
    >
    >
    > On Tue, 7 Feb 2006, Eric Dumazet wrote:
    > >
    > > This patch assumes that cpu_possible_map is setup before
    > > setup_per_cpu_areas().
    > >
    > > That sounds a reasonable assumption, but maybe not on your architecture ?
    >
    > I have to say, it sounds not just like a reasonable assumption, but like
    > the only sane assumption that there _could_ be.
    >
    > > I dont think cpu_possible_map has to be filled at smp_prepare_cpus() time, but
    > > long before.
    > >
    > > On i386/x86_64/ia64, this is done from setup_arch() called from start_kernel()
    > > just before setup_per_cpu_areas()
    > >
    > > On powerpc it's done from setup_system(), called before start_kernel()
    >
    > It absolutely _has_ to be done from setup_arch() or earlier, as shown by
    > the fact that "setup_per_cpu_areas()" is the very next thing that
    > init/main.c calls (and clearly, that needs to know what CPU's are
    > possible).
    >
    > ppc64 certainly calls it early enough, as does x86/x86-64/ia64. I don't
    > see anybody else doing it too late either.
    >
    > Heiko, can you point to the "old comment" you mentioned in the email, or
    > the architecture that does this wrong?
    >

    This one:

    --- devel/fs/file.c~reduce-size-of-percpudata-and-make-sure-per_cpuobject 2006-02-04 23:27:17.000000000 -0800
    +++ devel-akpm/fs/file.c 2006-02-04 23:27:17.000000000 -0800
    @@ -379,7 +379,6 @@ static void __devinit fdtable_defer_list
    void __init files_defer_init(void)
    {
    int i;
    - /* Really early - can't use for_each_cpu */
    - for (i = 0; i < NR_CPUS; i++)
    + for_each_cpu(i)
    fdtable_defer_list_init(i);
    }
    And yes, me too - when I saw that comment disappear I checked and decided
    that the comment was both wrong and undesirable.
    -
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