MFC r320561,r323236,r324041,r324314,r324609,r324613,r324778,r324780,r324787,

MFC r320561,r323236,r324041,r324314,r324609,r324613,r324778,r324780,r324787,
    r324803,r324836,r325469,r325706,r325917,r325918,r325919,r325920,r325921,
    r325922,r325925,r325963,r326106,r326107,r326110,r326111,r326112,r326194,
    r326195,r326196,r326197,r326198,r326199,r326200,r326237:

    rwlock: perform the typically false td_rw_rlocks check later

    Check if the lock is available first instead.

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    Sprinkle __read_frequently on few obvious places.

    Note that some of annotated variables should probably change their types
    to something smaller, preferably bit-sized.

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    mtx: drop the tid argument from _mtx_lock_sleep

    tid must be equal to curthread and the target routine was already reading
    it anyway, which is not a problem. Not passing it as a parameter allows for
    a little bit shorter code in callers.

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    locks: partially tidy up waiting on readers

    spin first instant of instantly re-readoing and don't re-read after
    spinning is finished - the state is already known.

    Note the code is subject to significant changes later.

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    locks: take the number of readers into account when waiting

    Previous code would always spin once before checking the lock. But a lock
    with e.g. 6 readers is not going to become free in the duration of once spin
    even if they start draining immediately.

    Conservatively perform one for each reader.

    Note that the total number of allowed spins is still extremely small and is
    subject to change later.

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    mtx: change MTX_UNOWNED from 4 to 0

    The value is spread all over the kernel and zeroing a register is
    cheaper/shorter than setting it up to an arbitrary value.

    Reduces amd64 GENERIC-NODEBUG .text size by 0.4%.

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    mtx: fix up owner_mtx after r324609

    Now that MTX_UNOWNED is 0 the test was alwayas false.

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    mtx: clean up locking spin mutexes

    1) shorten the fast path by pushing the lockstat probe to the slow path
    2) test for kernel panic only after it turns out we will have to spin,
    in particular test only after we know we are not recursing

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    mtx: stop testing SCHEDULER_STOPPED in kabi funcs for spin mutexes

    There is nothing panic-breaking to do in the unlock case and the lock
    case will fallback to the slow path doing the check already.

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    rwlock: reduce lockstat branches in the slowpath

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    mtx: fix up UP build after r324778

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    mtx: implement thread lock fastpath

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    rwlock: fix up compilation without KDTRACE_HOOKS after r324787

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    rwlock: use fcmpset for setting RW_LOCK_WRITE_SPINNER

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    sx: avoid branches if in the slow path if lockstat is disabled

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    rwlock: avoid branches in the slow path if lockstat is disabled

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    locks: pull up PMC_SOFT_CALLs out of slow path loops

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    mtx: unlock before traversing threads to wake up

    This shortens the lock hold time while not affecting corretness.
    All the woken up threads end up competing can lose the race against
    a completely unrelated thread getting the lock anyway.

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    rwlock: unlock before traversing threads to wake up

    While here perform a minor cleanup of the unlock path.

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    sx: perform a minor cleanup of the unlock slowpath

    No functional changes.

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    mtx: add missing parts of the diff in r325920

    Fixes build breakage.

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    locks: fix compilation issues without SMP or KDTRACE_HOOKS

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    locks: remove the file + line argument from internal primitives when not used

    The pair is of use only in debug or LOCKPROF kernels, but was passed (zeroed)
    for many locks even in production kernels.

    While here whack the tid argument from wlock hard and xlock hard.

    There is no kbi change of any sort - "external" primitives still accept the
    pair.

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    locks: pass the found lock value to unlock slow path

    This avoids an explicit read later.

    While here whack the cheaply obtainable 'tid' argument.

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    rwlock: don't check for curthread's read lock count in the fast path

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    rwlock: unbreak WITNESS builds after r326110

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    sx: unbreak debug after r326107

    An assertion was modified to use the found value, but it was not updated to
    handle a race where blocked threads appear after the entrance to the func.

    Move the assertion down to the area protected with sleepq lock where the
    lock is read anyway. This does not affect coverage of the assertion and
    is consistent with what rw locks are doing.

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    rwlock: stop re-reading the owner when going to sleep

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    locks: retry turnstile/sleepq loops on failed cmpset

    In order to go to sleep threads set waiter flags, but that can spuriously
    fail e.g. when a new reader arrives. Instead of unlocking everything and
    looping back, re-evaluate the new state while still holding the lock necessary
    to go to sleep.

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    sx: change sunlock to wake waiters up if it locked sleepq

    sleepq is only locked if the curhtread is the last reader. By the time
    the lock gets acquired new ones could have arrived. The previous code
    would unlock and loop back. This results spurious relocking of sleepq.

    This is a step towards xadd-based unlock routine.

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    rwlock: add __rw_try_{r,w}lock_int

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    rwlock: fix up compilation of the previous change

    commmitted wrong version of the patch

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    Convert in-kernel thread_lock_flags calls to thread_lock when debug is disabled

    The flags argument is not used in this case.

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    Add the missing lockstat check for thread lock.

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    rw: fix runlock_hard when new readers show up

    When waiters/writer spinner flags are set no new readers can show up unless
    they already have a different rw rock read locked. The change in r326195 failed
    to take that into account - in presence of new readers it would spin until
    they all drain, which would be lead to trouble if e.g. they go off cpu and
    can get scheduled because of this thread.