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    SubjectRe: [PATCH] 2.5.21 Nonlinear CPU support
    Date
    In message <20020611.021043.04190747.davem@redhat.com> you write:
    > From: Rusty Russell <rusty@rustcorp.com.au>
    > Date: Tue, 11 Jun 2002 19:09:44 +1000
    >
    > In message <3D05A9E8.FF0DA223@zip.com.au> you write:
    > > and slowdown:
    >
    > ARGH! STOP IT! I realize it's 'leet to be continually worrying about
    > possible microoptimizations, but I challenge you to *measure* the
    > slowdown between:
    >
    > Regardless, his space arguments still hold.

    You can allocate based on cpu_possible(cpu) (which is in the
    next patch) if you like, but I think you're better off fixing the
    existing NR_CPUS bloat as well, and keeping all the code simple.

    > I don't like having everyone eat the overhead that hotplugging cpus
    > seem to entail.

    But there's an important difference between something which is
    simple and unoptimized, and something which is unoptimizable.

    > And remember, it's the anal "every microoptimization at all costs"
    > people that keep the kernel sane and from running out of control bloat
    > wise.

    But it also gave us crap like net/ipv4/route.c:ip_rt_acct_read() 8(

    I know *you* benchmark and read the asm during optimization, but it's
    quite clear that others are so scared of "bloat" criticism that they
    optimize without measuring the straightforward case *first*.

    Remember, to be cool:
    1) Use bitops and memory barriers not spinlocks,
    2) Use inlines everywhere,
    3) Use likely()/unlikely() on every branch
    4) Use prefetch() everywhere,
    5) Use gotos to minimize the path length
    6) __set_current_state() not set_current_state()
    7) Pass in current as a function param

    Rusty.
    --
    Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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