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    SubjectRe: Serious problem with ticket spinlocks on ia64
    Date
    On Friday 27 of August 2010 15:48:02 Hedi Berriche wrote:
    > On Fri, Aug 27, 2010 at 14:38 Petr Tesarik wrote:
    > | Hi everybody,
    > |
    > | SGI has recently experienced failures with the new ticket spinlock
    > | implementation. Hedi Berriche sent me a simple test case that can
    > | trigger the failure on the siglock.
    >
    > One more fact, the problem was introduced by commit
    >
    > commit 9d40ee200a527ce08ab8c793ba8ae3e242edbb0e
    > Author: Tony Luck <tony.luck@intel.com>
    > Date: Wed Oct 7 10:54:19 2009 -0700
    >
    > [IA64] Squeeze ticket locks back into 4 bytes.
    >
    > Reverting the patch makes the problem go away.
    >
    > IOW, and as far as testing shows, the first incarnation of the ticket locks
    > implementation on IA64 (commit 2c8696), the one that used 8 bytes, does not
    > exhibit this problem.

    I wouldn't be so sure about it. Given that I have only observed the problem
    when the spinlock value wraps around, then an 8-byte spinlock might only need
    much more time to trigger the bug.

    Just my two cents,
    Petr Tesarik
    L3 International
    Novell, Inc.


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