Messages in this thread |  | | | Date | Thu, 24 Mar 2005 11:45:54 +0100 | | From | Ingo Molnar <> | | Subject | Re: [patch] Real-Time Preemption, -RT-2.6.12-rc1-V0.7.41-07 |
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* Steven Rostedt <rostedt@goodmis.org> wrote:
> I also see this with non rt tasks causing a burst of schedules. > > 1. Process A runs and grabs lock L. then finishes its time slice. > 2. Process B runs and tries to grab Lock L. > 3. Process A runs and releases lock L. > 4. __up_mutex gives process B lock L. > 5. Process A tries to grab lock L. > 6. Process B runs and releases lock L. > 7. __up_mutex gives lock L to process A. > 8. Process B tries to grab lock L again. > 9. Process A runs... > > Here we have more unnecessary schedules. So the condition to grab a lock > should be: > > 1. not owned. > 2. partially owned, and the owner is not RT. > 3. partially owned but the owner is RT and so is the grabber, and the > grabber's priority is >= the owner's priority.
yeah, sounds good - but i'd not make any distinction between RT and non-RT tasks - just make the rule #3 distinction based on ->prio. In particular on UP a task should only run when its higher prio, so if a lock is 'partially owned' then the priority rule should always be true. (On SMP it's a bit more complex, there the priority rule could make a real difference.)
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