remove unused code

MFC after: 2 days

Turn PREEMPTION into a kernel option. Make sure that it's defined if
FULL_PREEMPTION is defined. Add a runtime warning to ULE if PREEMPTION is
enabled (code inspired by the PREEMPTION warning in ke

Turn PREEMPTION into a kernel option. Make sure that it's defined if
FULL_PREEMPTION is defined. Add a runtime warning to ULE if PREEMPTION is
enabled (code inspired by the PREEMPTION warning in kern_switch.c). This
is a possible MT5 candidate.

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Give the 4bsd scheduler the ability to wake up idle processors
when there is new work to be done.

MFC after: 5 days

Give setrunqueue() and sched_add() more of a clue as to
where they are coming from and what is expected from them.

MFC after: 2 days

Backout the previous backout (with scott's ok). sched_ule.c:1.122 is
believed to fix the problem with ULE that this change triggered.

Revert the previous change. It works great for 4BSD but causes major
problems for ULE. The reason is quite unknown and worrisome.

In maybe_preempt(), ignore threads that are in an inconsistent state. This
is an effective band-aid for at least some of the scheduler corruption seen
recently. The real fix will involve protecting

In maybe_preempt(), ignore threads that are in an inconsistent state. This
is an effective band-aid for at least some of the scheduler corruption seen
recently. The real fix will involve protecting threads while they are
inconsistent, and will come later.

Submitted by: julian

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Add a temporary debugging hack to detect a deadlock in setrunqueue(). This
is here so that we can gather stats on the nature of the recent rash of
hard lockups, and in this particular case panic the

Add a temporary debugging hack to detect a deadlock in setrunqueue(). This
is here so that we can gather stats on the nature of the recent rash of
hard lockups, and in this particular case panic the machine instead of
letting it deadlock forever.

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Make kg->kg_runnable actually count runnable threads in the ksegrp run queue
instead of only doing it sometimes.. This is not used outdide of debugging code
in the current code, but that will probabl

Make kg->kg_runnable actually count runnable threads in the ksegrp run queue
instead of only doing it sometimes.. This is not used outdide of debugging code
in the current code, but that will probably change.

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Increase the amount of data exported by KTR in the KTR_RUNQ setting.
This extra data is needed to really follow what is going on in the
threaded case.

Don't scare users with a warning about preemption being off when it isn't
yet safe to have on by default.

Pass a thread argument into cpu_critical_{enter,exit}() rather than
dereference curthread. It is called only from critical_{enter,exit}(),
which already dereferences curthread. This doesn't seem to

Pass a thread argument into cpu_critical_{enter,exit}() rather than
dereference curthread. It is called only from critical_{enter,exit}(),
which already dereferences curthread. This doesn't seem to affect SMP
performance in my benchmarks, but improves MySQL transaction throughput
by about 1% on UP on my Xeon.

Head nodding: jhb, bmilekic

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Remove the previous hack since it doesn't make a difference and is getting
in the way of debugging.

Disable the PREEMPTION-enabled code in critical_exit() that encourages
switching to a different thread. This is just a hack to try to improve
stability some more, but likely points closer to the rea

Disable the PREEMPTION-enabled code in critical_exit() that encourages
switching to a different thread. This is just a hack to try to improve
stability some more, but likely points closer to the real culprit.

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- Move TDF_OWEPREEMPT, TDF_OWEUPC, and TDF_USTATCLOCK over to td_pflags
since they are only accessed by curthread and thus do not need any
locking.
- Move pr_addr and pr_ticks out of struct uprof

- Move TDF_OWEPREEMPT, TDF_OWEUPC, and TDF_USTATCLOCK over to td_pflags
since they are only accessed by curthread and thus do not need any
locking.
- Move pr_addr and pr_ticks out of struct uprof (which is per-process)
and directly into struct thread as td_profil_addr and td_profil_ticks
as these variables are really per-thread. (They are used to defer an
addupc_intr() that was too "hard" until ast()).

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Update for the KDB framework:
o Make debugging code conditional upon KDB instead of DDB.
o Call kdb_enter() instead of Debugger().
o Call kdb_backtrace() instead of db_print_backtrace() or backtra

Update for the KDB framework:
o Make debugging code conditional upon KDB instead of DDB.
o Call kdb_enter() instead of Debugger().
o Call kdb_backtrace() instead of db_print_backtrace() or backtrace().

kern_mutex.c:
o Replace checks for db_active with checks for kdb_active and make
them unconditional.

kern_shutdown.c:
o s/DDB_UNATTENDED/KDB_UNATTENDED/g
o s/DDB_TRACE/KDB_TRACE/g
o Save the TID of the thread doing the kernel dump so the debugger
knows which thread to select as the current when debugging the
kernel core file.
o Clear kdb_active instead of db_active and do so unconditionally.
o Remove backtrace() implementation.

kern_synch.c:
o Call kdb_reenter() instead of db_error().

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Unbreak build for the the !PREEMPTION case: don't define variables
that aren't used in that case.

Implement preemption of kernel threads natively in the scheduler rather
than as one-off hacks in various other parts of the kernel:
- Add a function maybe_preempt() that is called from sched_add() to

Implement preemption of kernel threads natively in the scheduler rather
than as one-off hacks in various other parts of the kernel:
- Add a function maybe_preempt() that is called from sched_add() to
determine if a thread about to be added to a run queue should be
preempted to directly. If it is not safe to preempt or if the new
thread does not have a high enough priority, then the function returns
false and sched_add() adds the thread to the run queue. If the thread
should be preempted to but the current thread is in a nested critical
section, then the flag TDF_OWEPREEMPT is set and the thread is added
to the run queue. Otherwise, mi_switch() is called immediately and the
thread is never added to the run queue since it is switch to directly.
When exiting an outermost critical section, if TDF_OWEPREEMPT is set,
then clear it and call mi_switch() to perform the deferred preemption.
- Remove explicit preemption from ithread_schedule() as calling
setrunqueue() now does all the correct work. This also removes the
do_switch argument from ithread_schedule().
- Do not use the manual preemption code in mtx_unlock if the architecture
supports native preemption.
- Don't call mi_switch() in a loop during shutdown to give ithreads a
chance to run if the architecture supports native preemption since
the ithreads will just preempt DELAY().
- Don't call mi_switch() from the page zeroing idle thread for
architectures that support native preemption as it is unnecessary.
- Native preemption is enabled on the same archs that supported ithread
preemption, namely alpha, i386, and amd64.

This change should largely be a NOP for the default case as committed
except that we will do fewer context switches in a few cases and will
avoid the run queues completely when preempting.

Approved by: scottl (with his re@ hat)

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- style fixes to the critical_exit() KASSERT().

Submitted by: bde

Move KASSERT regarding td_critnest to after the value of td is set to
curthread, to avoid warning and incorrect behavior.

Hoped not to mind: jeff

- Assert that td_critnest > 0 in critical_exit() to catch cases of
unbalanced uses of the critical_* api.

Although sometimes to the uninitiated, it may seem like goup, KSEGOUP
is actually spelt KSEGROUP. Go figure.

Reported by: samy@kerneled.com

Initial landing of SMP support for FreeBSD/amd64.

- This is heavily derived from John Baldwin's apic/pci cleanup on i386.
- I have completely rewritten or drastically cleaned up some other parts.

Initial landing of SMP support for FreeBSD/amd64.

- This is heavily derived from John Baldwin's apic/pci cleanup on i386.
- I have completely rewritten or drastically cleaned up some other parts.
(in particular, bootstrap)
- This is still a WIP. It seems that there are some highly bogus bioses
on nVidia nForce3-150 boards. I can't stress how broken these boards
are. I have a workaround in mind, but right now the Asus SK8N is broken.
The Gigabyte K8NPro (nVidia based) is also mind-numbingly hosed.
- Most of my testing has been with SCHED_ULE. SCHED_4BSD works.
- the apic and acpi components are 'standard'.
- If you have an nVidia nForce3-150 board, you are stuck with 'device
atpic' in addition, because they somehow managed to forget to connect the
8254 timer to the apic, even though its in the same silicon! ARGH!
This directly violates the ACPI spec.

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- Remove the correct thread from the run queue in setrunqueue(). This
fixes ULE + KSE.

- Update the sched api. sched_{add,rem,clock,pctcpu} now all accept a td
argument rather than a kse.