On Wed, 9 Mar 2016 13:24:23 +0100
Sebastian Andrzej Siewior [off-list ref] wrote:

* Josh Cartwright | 2016-03-08 12:26:56 [-0600]:

quoted

Is it really just about latency?  Does this deferral not lead to an
inversion in the case where the single woken task isn't the highest
priority waiter on the completion (and doesn't run due to a
middle-priority thing spinning)?  

This would be case, yes. Not only with deferral. Say you have two
waters: 1st one is MID-prio and the second is HI-prio. Currently after
the wakeup of the MID-prio waiter you get preempted. Waking all of them
at once would put the second waiter first on the CPU.
Samething without the deferral flag.

quoted

In order for this to work, it seems like the chosen waiter would need to
inherit the highest priority of all waiters (which AFAICT isn't
happening).  

sorting the waiters by priority? This will be fun. This is only done for
the rtmutex waiters.

Hmm, perhaps we should use an rbtree to sort simple waiters by
priority :-)

Probably wont make them simple anymore.

-- Steve