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    SubjectRe: [RFC PATCH 0/6] module, kbuild: Faster boot with custom kernel.
    On Wed, Feb 18, 2009 at 12:57, Rusty Russell <> wrote:
    > On Wednesday 18 February 2009 19:45:21 Kay Sievers wrote:

    >> The current load_module() wraps ~400 lines of pretty heavy code in
    >> stop_machine(), if we could possibly make that window smaller, so that
    >> multiple instances could prepare some of the work in parallel, and
    >> only a fraction of the current work would need to be serialized?
    > Module load doesn't use stop_machine (on non-error).

    I see, right. It's only the mutex serializing all module loading work.

    > I'm not sure where the code is spending time. We could shuffle things around
    > so most of load_module doesn't run under the lock, but before that can you tell
    > me if we still lose 2-3 seconds on a UP kernel?

    I tried only my dual core laptop with my "small" kernel and 50
    modules, not the crazy distro setup.

    I've added stuff like:
    ktime_t in, delta;
    unsigned long long duration;

    in = ktime_get();


    delta = ktime_sub(ktime_get(), in);
    duration = (unsigned long long) delta.tv64 >> 10;
    printk("XXX: loading %p (%Ld usecs)\n", umod, duration);

    across init_module() and some modules wait for 200-500 milliseconds to
    get the lock released, some larger modules spend 50 milliseconds in
    load_module(), many of them around 20 milliseconds.

    > If so, it's not locking, I'd guess it's probably modprobe userspace and reading in
    > the modules from disk, not sys_init_module at all.

    Bootcharts suggest that it's not I/O bound. We also see this on fast
    SSDs and with pre-loading files into RAM. Older modprobe versions did
    some heavy fnmatch() over an insanely large distro module.alias file,
    which was very CPU expensive, but that got changed recently.


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      Last update: 2009-02-18 15:01    [W:0.024 / U:15.500 seconds]
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