[LITMUS^RT] Proposed Feather-Trace / P-FP patches and misc fixes

[Björn Brandenburg]

Hi everyone,

I've pushed a couple of prop/ branches with cleaned-up RTAS work. All of the below patches are compile-tested and, at least before rebasing, ran fine on my machine.

1) https://github.com/LITMUS-RT/litmus-rt/commits/prop/sync-release

	d245619 Remove complete_n() API
	56faaa8 Re-implement synchronous task set release support

This branch reworks how Litmus does synchronous releases, which in the old implementation could cause latency spikes under partitioned schedulers.

2) https://github.com/LITMUS-RT/litmus-rt/commits/prop/fdso-cleanup

	4cb2ad2 FDSO: make sure fdso_close() is called during task teardown

This patch simply ensures that the destructors for semaphores are called when tasks "forget" to close them before termination.

3) https://github.com/LITMUS-RT/litmus-rt/commits/prop/feather-trace

This branch adds a lot of improvements to Feather-Trace overhead tracing.

	d940d73 Move SEND_RESCHED tracing to preempt.c
	ce313ac Move SCHED2 trace points to post_schedule()

The above two patches move trace points around. SCHED2 was at the wrong place, and SEND_RESCHED should be easier to maintain now.

The following patches improve detection of outliers due to interrupts and preemptions. As a result, it is no longer needed to use statistical outlier filtering (more details in Section V of https://www.mpi-sws.org/~bbb/papers/pdf/preprint-LP-locking-analysis.pdf). I'll push the matching changes to feather-trace-tools soon.

	a481c27 Feather-Trace: hide irq in SEND_RESCHED_END
	a13904d Trace IPI-related IRQs with ft_irq_fired()
	1ae3a8f Mark feather-trace buffers as "disturbed" on soft IRQs
	b1a59c1 Make Feather-Trace timestamp collection non-preemptive
	00b4b17 Use user-provided irq count for TS_SYSCALL_IN_END
	173e46b Export IRQ count to control page
	80e2d84 Feather-Trace: add support for locking-related syscall overheads
	5454446 Feather-Trace: update locking timestamps
	7b84800 Feather-Trace: keep track of PID in trace record

Finally, the following patch allows access to ftdev devices from multiple tasks.

	676bcd5 ftdev: don't hold lock while sleeping

4) https://github.com/LITMUS-RT/litmus-rt/commits/prop/pfp-fixes

This is collection of fixes and cleanups in the P-FP plugin.

	f0785d8 P-FP: be less permissive about non-running tasks in queue
	9e6b747 P-FP: be paranoid in the preemption case
	3e49128 P-FP: use proper CONFIG_ symbol
	057dcfd P-FP: prevent misuse of priority queue
	3e4922f P-FP: simplify priority comparison
	a5797a7 P-FP: simplify boost_priority()
	3ede287 P-FP: record job release records for tardy tasks

Please have a look the proposed patches over the next week or so (after the EuroSys deadline).  If there are no objections, I'd like to merge these changes soon.

Thanks,
Björn