Don't hold the scheduler lock while doing context switches. Instead we
unlock after selecting the new thread and switch within a spinlock
section leaving interrupts and preemption disabled to prevent local
concurrency. This means that mi_switch() is entered with the thread
locked but returns without. This dramatically simplifies scheduler
locking because we will not hold the schedlock while spinning on
blocked lock in switch.
This change has not been made to 4BSD but in principle it would be
more straightforward.
Discussed with: markj
Reviewed by: kib
Tested by: pho
Differential Revision: https://reviews.freebsd.org/D22778
Eliminate lock recursion from turnstiles. This was simply used to avoid
tracking the top-level turnstile lock. explicitly check for it before
picking up and dropping locks.
Reviewed by: kib
Tested by: pho
Differential Revision: https://reviews.freebsd.org/D22746
Eliminate recursion from most thread_lock consumers. Return from
sched_add() without the thread_lock held. This eliminates unnecessary
atomics and lock word loads as well as reducing the hold time for
scheduler locks. This will eventually allow for lockless remote adds.
Discussed with: kib
Reviewed by: jhb
Tested by: pho
Differential Revision: https://reviews.freebsd.org/D22626
turnstile_{lock,unlock}() were added for use in epoch. turnstile_lock()
returned NULL to indicate that the calling thread had lost a race and
the turnstile was no longer associated with the given lock, or the lock
owner. However, reader-writer locks may not have a designated owner,
in which case turnstile_lock() would return NULL and
epoch_block_handler_preempt() would leak spinlocks as a result.
Apply a minimal fix: return the lock owner as a separate return value.
Reviewed by: kib
MFC after: 3 days
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D21048
Code walks the list of contested turnstiles to calculate the priority
to unlend.
Reviewed by: markj
Tested by: pho
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Read locking is over used in the kernel to guarantee liveness. This API makes
it easy to provide livenes guarantees without atomics.
Includes epoch_test kernel module to stress test the API.
Documentation will follow initial use case.
Test case and improvements to preemption handling in response to discussion
with mjg@
Reviewed by: imp@, shurd@
Approved by: sbruno@
Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.
The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.
A follow-up to r322836.
Warnings for the unused declaration were breaking some second tier
architectures, but did not show up in Clang on x86.
Reported by: markj (ddb.4), emaste (declaration)
Sponsored by: Dell EMC Isilon
When debugging a deadlock, it is useful to follow the full chain of locks as
far as possible.
Reviewed by: jhb
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D12115
The replacement started at r283088 was necessarily incomplete without
replacing boolean_t with bool. This also involved cleaning some type
mismatches and ansifying old C function declarations.
Pointed out by: bde
Discussed with: bde, ian, jhb
In its stead use the Solaris / illumos approach of emulating '-' (dash)
in probe names with '__' (two consecutive underscores).
Reviewed by: markj
MFC after: 3 weeks
option, unbreak the lock tracing release semantic by embedding
calls to LOCKSTAT_PROFILE_RELEASE_LOCK() direclty in the inlined
version of the releasing functions for mutex, rwlock and sxlock.
Failing to do so skips the lockstat_probe_func invokation for
unlocking.
- As part of the LOCKSTAT support is inlined in mutex operation, for
kernel compiled without lock debugging options, potentially every
consumer must be compiled including opt_kdtrace.h.
Fix this by moving KDTRACE_HOOKS into opt_global.h and remove the
dependency by opt_kdtrace.h for all files, as now only KDTRACE_FRAMES
is linked there and it is only used as a compile-time stub [0].
[0] immediately shows some new bug as DTRACE-derived support for debug
in sfxge is broken and it was never really tested. As it was not
including correctly opt_kdtrace.h before it was never enabled so it
was kept broken for a while. Fix this by using a protection stub,
leaving sfxge driver authors the responsibility for fixing it
appropriately [1].
Sponsored by: EMC / Isilon storage division
Discussed with: rstone
[0] Reported by: rstone
[1] Discussed with: philip
Idle threads are not allowed to acquire any lock but spinlocks.
Deny any attempt to do so by panicing at the locking operation
when INVARIANTS is on. Then, remove the check on blocking on a
turnstile.
The check in sleepqueues is left because they are not allowed to use
tsleep() either which could happen still.
Reviewed by: bde, jhb, kib
MFC after: 1 week
compatible with the sched provider implemented by Solaris and its open-
source derivatives. Full documentation of the sched provider can be found
on Oracle's DTrace wiki pages.
Note that for compatibility with scripts originally written for Solaris,
serveral probes are defined that will never fire. These probes are defined
to fire when Solaris-specific features perform certain actions. As these
features are not present in FreeBSD, the probes can never fire.
Also, I have added a two probes that are not defined in Solaris, lend-pri
and load-change. These probes have been added to make it possible to
collect schedgraph data with DTrace.
Finally, a few probes are defined in Solaris to take a cpuinfo_t *
argument. As it was not immediately clear to me how to translate that to
FreeBSD, currently those probes are passed NULL in place of a cpuinfo_t *.
Sponsored by: Sandvine Incorporated
MFC after: 2 weeks
backtrace for an arbitrary thread (rather than the calling thread).
A kdb_backtrace_thread() wrapper function uses the configured debugger
if possible, otherwise it falls back to using stack(9) if that is
available.
- Replace a direct call to db_trace_thread() in propagate_priority()
with a call to kdb_backtrace_thread() instead.
MFC after: 1 week
The SYSCTL_NODE macro defines a list that stores all child-elements of
that node. If there's no SYSCTL_DECL macro anywhere else, there's no
reason why it shouldn't be static.
While the name is pretentious, a good explanation of its targets is
reported in this 17 months old presentation e-mail:
http://lists.freebsd.org/pipermail/freebsd-arch/2008-August/008452.html
In order to implement it, the sq_type in sleepqueues is mandatory and not
only compiled along with INVARIANTS option. Additively, a new sleepqueue
function, sleepq_type() is added, returning the type of the sleepqueue
linked to a wchan.
Three new sysctls are added in order to configure the thread:
debug.deadlkres.slptime_threshold
debug.deadlkres.blktime_threshold
debug.deadlkres.sleepfreq
rappresenting the thresholds for sleep and block time that will lead to
a deadlock matching (when exceeded), while the sleepfreq rappresents the
number of seconds between 2 consecutive thread runnings.
In order to enable the deadlock resolver thread recompile your kernel
with the option DEADLKRES.
Reviewed by: jeff
Tested by: pho, Giovanni Trematerra
Sponsored by: Nokia Incorporated, Sandvine Incorporated
MFC after: 2 weeks
the command set (only so long as the module is present):
o add db_command_register and db_command_unregister to add and remove
commands, respectively
o replace linker sets with SYSINIT's (and SYSUINIT's) that register
commands
o expose 3 list heads: db_cmd_table, db_show_table, and db_show_all_table
for registering top-level commands, show operands, and show all operands,
respectively
While here also:
o sort command lists
o add DB_ALIAS, DB_SHOW_ALIAS, and DB_SHOW_ALL_ALIAS to add aliases
for existing commands
o add "show all trace" as an alias for "show alltrace"
o add "show all locks" as an alias for "show alllocks"
Submitted by: Guillaume Ballet <gballet@gmail.com> (original version)
Reviewed by: jhb
MFC after: 1 month
- Set UMA_ZONE_NOFREE so that the per-turnstile spin locks are type stable
to avoid a race where one thread might dereference a lock in a free'd
turnstile that was previously used by another thread.
Theorized by: tegge (2)
MFC after: 1 week
variables and sysctl nodes.
- In reset walk the children of kern_sched_stats and reset the counters
via the oid_arg1 pointer. This allows us to add arbitrary counters to
the tree and still reset them properly.
- Define a set of switch types to be passed with flags to mi_switch().
These types are named SWT_*. These types correspond to SCHED_STATS
counters and are automatically handled in this way.
- Make the new SWT_ types more specific than the older switch stats.
There are now stats for idle switches, remote idle wakeups, remote
preemption ithreads idling, etc.
- Add switch statistics for ULE's pickcpu algorithm. These stats include
how much migration there is, how often affinity was successful, how
often threads were migrated to the local cpu on wakeup, etc.
Sponsored by: Nokia
the provided lock or &blocked_lock. The thread may be temporarily
assigned to the blocked_lock by the scheduler so a direct comparison
can not always be made.
- Use THREAD_LOCKPTR_ASSERT() in the primary consumers of the scheduling
interfaces. The schedulers themselves still use more explicit asserts.
Sponsored by: Nokia
- Move recursion checking into rwlock inlines to free a bit for use with
adaptive spinners.
- Clear the RW_LOCK_WRITE_SPINNERS flag whenever the lock state changes
causing write spinners to restart their loop.
- Write spinners are limited by a count while readers hold the lock as
there is no way to know for certain whether readers are running still.
- In the read path block if there are write waiters or spinners to avoid
starving writers. Use a new per-thread count, td_rw_rlocks, to skip
starvation avoidance if it might cause a deadlock.
- Remove or change invalid assertions in turnstiles.
Reviewed by: attilio (developed parts of the patch as well)
Sponsored by: Nokia
opposed to what process. Since threads by default have teh name of the
process unless over-written with more useful information, just print the
thread name instead.
- Add a per-turnstile spinlock to solve potential priority propagation
deadlocks that are possible with thread_lock().
- The turnstile lock order is defined as the exact opposite of the
lock order used with the sleep locks they represent. This allows us
to walk in reverse order in priority_propagate and this is the only
place we wish to multiply acquire turnstile locks.
- Use the turnstile_chain lock to protect assigning mutexes to turnstiles.
- Change the turnstile interface to pass back turnstile pointers to the
consumers. This allows us to reduce some locking and makes it easier
to cancel turnstile assignment while the turnstile chain lock is held.
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)
speedup and will be more useful after each gains a spinlock in the
impending thread_lock() commit.
- Move initialization and asserts into init/fini routines. fini routines
are only needed in the INVARIANTS case for now.
Submitted by: Attilio Rao <attilio@FreeBSD.org>
Tested by: kris, jeff
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}.
preemptions when adjusting the priority of a thread that is on a run
queue. This was only observed when FULL_PREEMPTION was enabled.
Reported by: kris
Diagnosed by: ups
MFC after: 1 week
that it operates on lockmgr and sx locks. This can be useful for tracking
down vnode deadlocks in VFS for example. Note that this command is a bit
more fragile than 'show lockchain' as we have to poke around at the
wait channel of a thread to see if it points to either a struct lock or
a condition variable inside of a struct sx. If td_wchan points to
something unmapped, then this command will terminate early due to a fault,
but no harm will be done.
'show lockchain'. The churn is because I'm about to add a new
'show sleepchain' similar to 'show lockchain' for sleep locks (lockmgr and
sx) and 'show threadchain' was a bit ambiguous as both commands show
a chain of thread dependencies, 'lockchain' is for non-sleepable locks
(mtx and rw) and 'sleepchain' is for sleepable locks.
problems in ddb:
- "show threadchain [thread]" will start with the specified thread (or the
current kdb thread by default) and show it's state. If it is blocked on
a lock, it will find the owner of the lock and show its state, etc.
- "show allchains" will find all of the threads that are blocked on a
lock (but do not have any threads blocked on a lock they hold) and show
the resulting thread chain.
- "show lockchain <lock>" takes a pointer to a lock_object (such as a
mutex or rwlock). If there is a turnstile for that lock, then it will
display all the threads blocked on the lock. In addition, for each
thread blocked on the lock, it will display any contested locks they
hold, and recurse on those locks to show any threads blocked on those
locks, etc.
a lock's priority to a sleeping thread. When we panic, dump a stack
trace of the thread that is asleep if DDB is compiled into the kernel
just before calling panic(). This is much more informative and useful
for debugging than the current behavior of getting a page fault and not
having an easy way of determining which thread caused the original problem.
MFC after: 1 week
each turnstile. Also, allow for the owner thread pointer of a turnstile
to be NULL. This is needed for the upcoming reader/writer lock
implementation.
- Add a new ddb command 'show turnstile' that will look up the turnstile
associated with the given lock argument and display useful information
like the list of threads blocked on each queue, etc. If there isn't an
active turnstile for a lock at the specified address, then the function
will see if there is an active turnstile at the specified address and
display info about it if so.
- Adjust the mutex code to handle the turnstile API changes.
Tested on: i386 (all), alpha, amd64, sparc64 (1 and 3)
