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    SubjectRe: [PATCH] Significant performace improvements on reiserfs systems
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    On Thu, 2001-09-20 at 21:20, Andrew Morton wrote:
    > This may not be practical.
    >
    > Take, for example, zap_page_range(). It simply has a lot
    > of work to do, and it does it inside a spinlock. By doing
    > it in a tight loop, it's optimal.
    >
    > There is no way to speed this function up by two or three orders
    > of magnitude. (Well, there is: don't take the lock at all if
    > the mm isn't shared, but this is merely an example. There are
    > other instances).

    Agreed, but...

    > It seems that for a preemptive kernel to be successful, we need
    > to globally alter the kernel so that it never holds locks for
    > more than 500 microseconds. Which is what the conditional_schedule()
    > (aka cooperative multitasking :)) patches do.
    >
    > It seems that there are no magic bullets, and low latency will
    > forever have a global impact on kernel design, unless a way is
    > found to reschedule with locks held. I recall that a large
    > part of the MontaVista patch involved turning spinlocks into
    > semaphores, yes? That would seem to be the way to go.

    This would be the situation that solved the problem with little
    complaint, huh?

    --
    Robert M. Love
    rml at ufl.edu
    rml at tech9.net

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