- Garbage collect unused concurrency functions.

Commit 1/14 of sched_lock decomposition.
- Move all scheduler locking into the schedulers utilizing a technique
similar to solaris's container locking.
- A per-process spinlock is now used to pr

Commit 1/14 of sched_lock decomposition.
- Move all scheduler locking into the schedulers utilizing a technique
similar to solaris's container locking.
- A per-process spinlock is now used to protect the queue of threads,
thread count, suspension count, p_sflags, and other process
related scheduling fields.
- The new thread lock is actually a pointer to a spinlock for the
container that the thread is currently owned by. The container may
be a turnstile, sleepqueue, or run queue.
- thread_lock() is now used to protect access to thread related scheduling
fields. thread_unlock() unlocks the lock and thread_set_lock()
implements the transition from one lock to another.
- A new "blocked_lock" is used in cases where it is not safe to hold the
actual thread's lock yet we must prevent access to the thread.
- sched_throw() and sched_fork_exit() are introduced to allow the
schedulers to fix-up locking at these points.
- Add some minor infrastructure for optionally exporting scheduler
statistics that were invaluable in solving performance problems with
this patch. Generally these statistics allow you to differentiate
between different causes of context switches.

Tested by: kris, current@
Tested on: i386, amd64, ULE, 4BSD, libthr, libkse, PREEMPTION, etc.
Discussed with: kris, attilio, kmacy, jhb, julian, bde (small parts each)

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- Change types for necent runq additions to u_char rather than int.
- Fix these types in ULE as well. This fixes bugs in priority index
calculations in certain edge cases. (int)-1 % 64 != (uint)

- Change types for necent runq additions to u_char rather than int.
- Fix these types in ULE as well. This fixes bugs in priority index
calculations in certain edge cases. (int)-1 % 64 != (uint)-1 % 64.

Reported by: kkenn using pho's stress2.

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- Remove setrunqueue and replace it with direct calls to sched_add().
setrunqueue() was mostly empty. The few asserts and thread state
setting were moved to the individual schedulers. sched_a

- Remove setrunqueue and replace it with direct calls to sched_add().
setrunqueue() was mostly empty. The few asserts and thread state
setting were moved to the individual schedulers. sched_add() was
chosen to displace it for naming consistency reasons.
- Remove adjustrunqueue, it was 4 lines of code that was ifdef'd to be
different on all three schedulers where it was only called in one place
each.
- Remove the long ifdef'd out remrunqueue code.
- Remove the now redundant ts_state. Inspect the thread state directly.
- Don't set TSF_* flags from kern_switch.c, we were only doing this to
support a feature in one scheduler.
- Change sched_choose() to return a thread rather than a td_sched. Also,
rely on the schedulers to return the idlethread. This simplifies the
logic in choosethread(). Aside from the run queue links kern_switch.c
mostly does not care about the contents of td_sched.

Discussed with: julian

- Move the idle thread loop into the per scheduler area. ULE wants to
do something different from the other schedulers.

Suggested by: jhb

Tested on: x86/amd64 sched_{4BSD, ULE, CORE}.

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- Don't pass a pointer into runq_choose_from(). The caller can adjust the
index if it chooses to.

- Add three new functions to support circular run queues.
- runq_add_pri allows the caller to position the thread at any rqindex
regardless of priority.
- runq_choose_from() chooses the lowest p

- Add three new functions to support circular run queues.
- runq_add_pri allows the caller to position the thread at any rqindex
regardless of priority.
- runq_choose_from() chooses the lowest priority thread starting from a given
index. The index is updated with the rqindex of the chosen thread. This
routine is used to pick the lowest priority relative to a given index.
- runq_remove_idx() updates the index if the run queue that held the removed
thread is now empty.

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Prefer a more traditional spelling of inhibited in comments and panic
messages.

Threading cleanup.. part 2 of several.

Make part of John Birrell's KSE patch permanent..
Specifically, remove:
Any reference of the ksegrp structure. This feature was
never fully utilised and made t

Threading cleanup.. part 2 of several.

Make part of John Birrell's KSE patch permanent..
Specifically, remove:
Any reference of the ksegrp structure. This feature was
never fully utilised and made things overly complicated.
All code in the scheduler that tried to make threaded programs
fair to unthreaded programs. Libpthread processes will already
do this to some extent and libthr processes already disable it.

Also:
Since this makes such a big change to the scheduler(s), take the opportunity
to rename some structures and elements that had to be moved anyhow.
This makes the code a lot more readable.

The ULE scheduler compiles again but I have no idea if it works.

The 4bsd scheduler still reqires a little cleaning and some functions that now do
ALMOST nothing will go away, but I thought I'd do that as a separate commit.

Tested by David Xu, and Dan Eischen using libthr and libpthread.

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Make KSE a kernel option, turned on by default in all GENERIC
kernel configs except sun4v (which doesn't process signals properly
with KSE).

Reviewed by: davidxu@

Add scheduler CORE, the work I have done half a year ago, recent,
I picked it up again. The scheduler is forked from ULE, but the
algorithm to detect an interactive process is almost completely
diffe

Add scheduler CORE, the work I have done half a year ago, recent,
I picked it up again. The scheduler is forked from ULE, but the
algorithm to detect an interactive process is almost completely
different with ULE, it comes from Linux paper "Understanding the
Linux 2.6.8.1 CPU Scheduler", although I still use same word
"score" as a priority boost in ULE scheduler.

Briefly, the scheduler has following characteristic:
1. Timesharing process's nice value is seriously respected,
timeslice and interaction detecting algorithm are based
on nice value.
2. per-cpu scheduling queue and load balancing.
3. O(1) scheduling.
4. Some cpu affinity code in wakeup path.
5. Support POSIX SCHED_FIFO and SCHED_RR.
Unlike scheduler 4BSD and ULE which using fuzzy RQ_PPQ, the scheduler
uses 256 priority queues. Unlike ULE which using pull and push, the
scheduelr uses pull method, the main reason is to let relative idle
cpu do the work, but current the whole scheduler is protected by the
big sched_lock, so the benefit is not visible, it really can be worse
than nothing because all other cpu are locked out when we are doing
balancing work, which the 4BSD scheduelr does not have this problem.
The scheduler does not support hyperthreading very well, in fact,
the scheduler does not make the difference between physical CPU and
logical CPU, this should be improved in feature. The scheduler has
priority inversion problem on MP machine, it is not good for
realtime scheduling, it can cause realtime process starving.
As a result, it seems the MySQL super-smack runs better on my
Pentium-D machine when using libthr, despite on UP or SMP kernel.

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sched_rem() already sets ke->ke_state to KES_THREAD, so there's no need
to redo it.

Trim trailing whitespace.

Restore KTR_CRITICAL but conditionally compile it in as KTR_SCHED.

Requested by: scottl, jhb

Clean up unused or poorly utilized KTR values. Remove KTR_FS, KTR_KGDB,
and KTR_IO as they were never used. Remove KTR_CLK since it was only
used for hardclock firing and use KTR_INTR there instead

Clean up unused or poorly utilized KTR values. Remove KTR_FS, KTR_KGDB,
and KTR_IO as they were never used. Remove KTR_CLK since it was only
used for hardclock firing and use KTR_INTR there instead. Remove
KTR_CRITICAL since it was only used for crit enter/exit and use
KTR_CONTENTION instead.

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In adjustrunqueue(), add code to handle thread migrating case for
ULE scheduler. In original code, local run queue of threaded ksegrp
is corrupted if adjustrunqueue() is called while thread is migrat

In adjustrunqueue(), add code to handle thread migrating case for
ULE scheduler. In original code, local run queue of threaded ksegrp
is corrupted if adjustrunqueue() is called while thread is migrating.

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Restore preemption of idle threads.

Submitted by: jhb

Lots of whitespace cleanup.
Fix for broken if condition.

Submitted by: nate@

Fix some race conditions for pinned threads that may cause them to run
on the wrong CPU.

Add IPI support for preempting a thread on another CPU.

MFC after:3 weeks

Use low level constructs borrowed from interrupt threads to wait for
work in proc0.
Remove the TDP_WAKEPROC0 workaround.

Fix a bug that caused preemption to happen for a thread in the same
ksegrp with the same priority as the currently running thread.
This can cause propagate_priority() to panic.

Pointy hat to: ups

Sprinkle some volatile magic and rearrange things a bit to avoid race
conditions in critical_exit now that it no longer blocks interrupts.

Reviewed by: jhb

Divorce critical sections from spinlocks. Critical sections as denoted by
critical_enter() and critical_exit() are now solely a mechanism for
deferring kernel preemptions. They no longer have any a

Divorce critical sections from spinlocks. Critical sections as denoted by
critical_enter() and critical_exit() are now solely a mechanism for
deferring kernel preemptions. They no longer have any affect on
interrupts. This means that standalone critical sections are now very
cheap as they are simply unlocked integer increments and decrements for the
common case.

Spin mutexes now use a separate KPI implemented in MD code: spinlock_enter()
and spinlock_exit(). This KPI is responsible for providing whatever MD
guarantees are needed to ensure that a thread holding a spin lock won't
be preempted by any other code that will try to lock the same lock. For
now all archs continue to block interrupts in a "spinlock section" as they
did formerly in all critical sections. Note that I've also taken this
opportunity to push a few things into MD code rather than MI. For example,
critical_fork_exit() no longer exists. Instead, MD code ensures that new
threads have the correct state when they are created. Also, we no longer
try to fixup the idlethreads for APs in MI code. Instead, each arch sets
the initial curthread and adjusts the state of the idle thread it borrows
in order to perform the initial context switch.

This change is largely a big NOP, but the cleaner separation it provides
will allow for more efficient alternative locking schemes in other parts
of the kernel (bare critical sections rather than per-CPU spin mutexes
for per-CPU data for example).

Reviewed by: grehan, cognet, arch@, others
Tested on: i386, alpha, sparc64, powerpc, arm, possibly more

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Add a read-only kern.sched.preemption sysctl so that user space can tell
if "options PREEMPTION" is compiled into the kernel.

A further step on the journey of meaking panics and debugging more reliable:
in the window between the beginning of panic() and entering the debugger,
it's possible to receive interrupts. If we rece

A further step on the journey of meaking panics and debugging more reliable:
in the window between the beginning of panic() and entering the debugger,
it's possible to receive interrupts. If we receive an interrupt, don't
preempt if panicstr != NULL, as the system is in the process of failing, and
the preempting thread is likely to stumble over the failure. The typical
scenario is during the printf() in panic() prior to entering the debugger,
but when running with a slower console type such as serial console.

It could be that the panic string should be passed to the debugger to print,
so that it can run from the debugger's environment rather than a regular
kernel printf.

Glanced at by: jhb

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