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    SubjectRe: dramatic I/O slowdown after upgrading 2.6.32->3.0
    On Fri, Apr 06, 2012 at 08:45:40AM +0400, Michael Tokarev wrote:
    > On 06.04.2012 03:29, Jan Kara wrote:
    >
    > > On Fri 30-03-12 20:50:54, Michael Tokarev wrote:
    > >> I'm observing a dramatic slowdown of several hosts after upgrading
    > >> from 2.6.32.y to 3.0.x i686 kernels (in both cases from kernel.org,
    > >> on both cases the last version is relatively latest).
    > []
    > >> What's the way to debug this issue?
    > > Identifying a particular kernel where things regresses might help as Jon
    > > wrote. Just from top of my head, 3.0 had a bug in device plugging so
    > > readahead was broken. I think it was addressed in -stable series so you
    >
    > That's definitely not readahead, it since writes are painfully slow
    > too. I found one more example -- extlinux --once="test kernel" with
    > 3.0 takes about 20 seconds to complete on an idle system.
    >
    > > might want to check out latest 3.0-stable.
    >
    > I did mention this in my initial email (that part quoted above) --
    > both 2.6.32 and 3.0 are relatively latest from each series,
    > right now it is 3.0.27.
    >
    > Yesterday I tried to do some bisection, but ended up in an unbootable
    > system (it is remote production server), so now I'm waiting for remote
    > hands to repair it (I don't yet know what went wrong, we'll figure it
    > out). I've some time during nights when I can do anything with that
    > machine, but I have to keep it reachable/working on each reboot.
    >
    > Apparently I was wrong saying that there's another machine which
    > suffers from the same issue -- nope, the other machine had an unrelated
    > issue which I fixed. So it turns out that from about 200 different
    > machines, I've just one machine which does not run 3.0 kernel properly.
    > I especially tried 3.0 on a few more - different - machines last
    > weekend, in order to see what other machines has this problem, but
    > found nothing.
    >
    > So I'll try to continue (or actually _start_) the bisection on this
    > very server, the way it will be possible having in mind the difficult
    > conditions.
    >
    > I just thoght I'd ask first, maybe someone knows offhand what may be
    > the problem.. ;)

    Barriers. Turn them off, and see if that fixes your problem.

    Cheers,

    Dave.
    --
    Dave Chinner
    david@fromorbit.com


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