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    SubjectRe: [BUG] long freezes on thinkpad t60


    On Thu, 21 Jun 2007, Ingo Molnar wrote:
    >
    > damn, i first wrote up an explanation about why that ugly __delay(1) is
    > there (it almost hurts my eyes when i look at it!) but then deleted it
    > as superfluous :-/

    I'm fine with a delay, but the __delay(1) is simply not "correct". It
    doesn't do anything.

    "udelay()" waits for a certain time. Use that.

    > the reason for the __delay(1) was really mundane: to be able to figure
    > out when to print a 'we locked up' message to the user.

    No it does not.

    You may think it does, but it does nothing of the sort.

    Use "udelay()" or somethign that actually takes a *time*.

    Just __delay() is nothing but a loop, and calling it with an argument of 1
    is stupid and buggy.

    The only *possibly* valid use of "__delay()" implies using a counter that
    is based on the "loops_per_sec" thing, which depends on what the delay
    function actually is.

    For example, the delay function may well turn out to be this:

    __asm__ __volatile__(
    "\tjmp 1f\n"
    ".align 16\n"
    "1:\tjmp 2f\n"
    ".align 16\n"
    "2:\tdecl %0\n\tjns 2b"
    :"=&a" (d0)
    :"0" (loops));

    Notice? "Your code, it does nothing!"

    When I said that the code was buggy, I meant it.

    It has nothing to do with spinlocks. And "__delay(1)" is *always* a bug.

    You migth want to replace it with

    smp_rmb();
    udelay(1);

    instead, at which point it *does* something: it has that read barrier
    (which is not actually needed on x86, but whatever), and it has a delay
    that is *meaningful*.

    A plain "__delay(1)" is neither.

    So let me repeat my statement: "What a piece of crap".

    Linus
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