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    SubjectRe: Recent kernel "mount" slow
    On 2012-11-27 06:57, Jeff Chua wrote:
    > On Sun, Nov 25, 2012 at 7:23 AM, Jeff Chua <jeff.chua.linux@gmail.com> wrote:
    >> On Sun, Nov 25, 2012 at 5:09 AM, Mikulas Patocka <mpatocka@redhat.com> wrote:
    >>> So it's better to slow down mount.
    >>
    >> I am quite proud of the linux boot time pitting against other OS. Even
    >> with 10 partitions. Linux can boot up in just a few seconds, but now
    >> you're saying that we need to do this semaphore check at boot up. By
    >> doing so, it's inducing additional 4 seconds during boot up.
    >
    > By the way, I'm using a pretty fast SSD (Samsung PM830) and fast CPU
    > (2.8GHz). I wonder if those on slower hard disk or slower CPU, what
    > kind of degradation would this cause or just the same?

    It'd likely be the same slow down time wise, but as a percentage it
    would appear smaller on a slower disk.

    Could you please test Mikulas' suggestion of changing
    synchronize_sched() in include/linux/percpu-rwsem.h to
    synchronize_sched_expedited()?

    linux-next also has a re-write of the per-cpu rw sems, out of Andrews
    tree. It would be a good data point it you could test that, too.

    In any case, the slow down definitely isn't acceptable. Fixing an
    obscure issue like block sizes changing while O_DIRECT is in flight
    definitely does NOT warrant a mount slow down.

    --
    Jens Axboe



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