[RFC][PATCH RT 0/2] futex priority based wakeup

["Sébastien Dugué" <sebastien.dugue@bull.net>]

  Hi,

  in the current futex implementation, tasks are woken up in FIFO order,
(i.e. in the order they were put to sleep). For realtime systems needing
system wide strict realtime priority scheduling, tasks should be woken up
in priority order.

  This patchset achieves this by changing the futex hash bucket list into
a plist. Tasks waiting on a futex are enqueued in this plist based on
their priority so that they can be woken up in priority order.

  The 1st patch is a small optimization to futex_requeue() which could
go into mainline and does not depend on the RT patch.

  The 2nd patch does the real job of converting the futex hash bucket list
into a plist.
  There is however a drawback with this patch in that it is not possible to use
CONFIG_DEBUG_PI_LIST as the plist debugging code expects the spinlock protecting
the plist to be a raw_spinlock while the futex hash bucket lock is a regular
spinlock (rt-mutex). Maybe the plist debugging checks could be made generic to
accept both types.

  Any thoughts?

  Comments welcomed.

  Sébastien.



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  Sébastien Dugué                BULL/FREC:B1-247
  phone: (+33) 476 29 77 70      Bullcom: 229-7770

  mailto:sebastien.dugue@bull.net

  Linux POSIX AIO: http://www.bullopensource.org/posix
                   http://sourceforge.net/projects/paiol
  
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