In the case of the thread being on a sleepqueue or a turnstile, the
sched_lock was acquired (without the aid of the td_lock interface) and
the td_lock was dropped. This was going to break locking rules on other
threads willing to access to the thread (via the td_lock interface) and
modify his flags (allowed as long as the container lock was different
by the one used in sched_switch).
In order to prevent this situation, while sched_lock is acquired there
the td_lock gets blocked. [0]
- Merge the ULE's internal function thread_block_switch() into the global
thread_lock_block() and make the former semantic as the default for
thread_lock_block(). This means that thread_lock_block() will not
disable interrupts when called (and consequently thread_unlock_block()
will not re-enabled them when called). This should be done manually
when necessary.
Note, however, that ULE's thread_unblock_switch() is not reaped
because it does reflect a difference in semantic due in ULE (the
td_lock may not be necessarilly still blocked_lock when calling this).
While asymmetric, it does describe a remarkable difference in semantic
that is good to keep in mind.
[0] Reported by: Kohji Okuno
<okuno dot kohji at jp dot panasonic dot com>
Tested by: Giovanni Trematerra
<giovanni dot trematerra at gmail dot com>
MFC: 2 weeks
is not cleaned up on the wakeup but reset.
This is harmless mostly because td_slptick (and ki_slptime from
userland) should be analyzed only with the assumption that the thread
is actually sleeping (thus while the td_slptick is correctly set) but
without this invariant the number is nomore consistent.
- Move td_slptick from u_int to int in order to follow 'ticks' signedness
and wrap up accordingly [0]
[0] Submitted by: emaste
Sponsored by: Sandvine Incorporated
MFC 1 week
or equial then PSOCK, not less or equial. Higher priority has lesser
numerical value.
Existing test does not allow for swapout of the thread waiting for
advisory lock, for exiting child or sleeping for timeout. On the other
hand, high-priority waiters of VFS/VM events can be swapped out.
Tested by: pho
Reviewed by: jhb
MFC after: 1 week
This improvements aims for avoiding further cache-misses in scheduler
specific functions which need to keep track of average thread running
time and further locking in places setting for this flag.
Reported by: jeff (originally), kris (currently)
Reviewed by: jhb
Tested by: Giuseppe Cocomazzi <sbudella at email dot it>
sizeof("MAXCPU") being used to calculate a string length rather than
something more reasonable such as sizeof("32"). This shouldn't have
caused any ill effect until we run on machines with 1000000 or more
cpus.
with src/tools/sched/schedgraph.py. This allows developers to quickly
create a graphical view of ktr data for any resource in the system.
- Add sched_tdname() and the pcpu field 'name' for quickly and uniformly
identifying records associated with a thread or cpu.
- Reimplement the KTR_SCHED traces using the new generic facility.
Obtained from: attilio
Discussed with: jhb
Sponsored by: Nokia
- When a cpuset is applied to a thread, walk the cpuset to see if it is a
"full" cpuset (includes all available CPUs). If not, set a new
TDS_AFFINITY flag to indicate that this thread can't run on all CPUs.
When inheriting a cpuset from another thread during thread creation, the
new thread also inherits this flag. It is in a new ts_flags field in
td_sched rather than using one of the TDF_SCHEDx flags because fork()
clears td_flags after invoking sched_fork().
- When placing a thread on a runqueue via sched_add(), if the thread is not
pinned or bound but has the TDS_AFFINITY flag set, then invoke a new
routine (sched_pickcpu()) to pick a CPU for the thread to run on next.
sched_pickcpu() walks the cpuset and picks the CPU with the shortest
per-CPU runqueue length. Note that the reason for the TDS_AFFINITY flag
is to avoid having to walk the cpuset and examine runq lengths in the
common case.
- To avoid walking the per-CPU runqueues in sched_pickcpu(), add an array
of counters to hold the length of the per-CPU runqueues and update them
when adding and removing threads to per-CPU runqueues.
MFC after: 2 weeks
from idle over the next tick.
- Add a new MD routine, cpu_wake_idle() to wakeup idle threads who are
suspended in cpu specific states. This function can fail and cause the
scheduler to fall back to another mechanism (ipi).
- Implement support for mwait in cpu_idle() on i386/amd64 machines that
support it. mwait is a higher performance way to synchronize cpus
as compared to hlt & ipis.
- Allow selecting the idle routine by name via sysctl machdep.idle. This
replaces machdep.cpu_idle_hlt. Only idle routines supported by the
current machine are permitted.
Sponsored by: Nokia
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
rqindex back in struct thread.
- Compile kern_switch.c independently again and stop #include'ing it from
schedulers.
- Remove the ts_thread backpointers and convert most code to go from
struct thread to struct td_sched.
- Cleanup the ts_flags #define garbage that was causing us to sometimes
do things that expanded to td->td_sched->ts_thread->td_flags in 4BSD.
- Export the kern.sched sysctl node in sysctl.h
is only used by 4bsd.
- Create a new runq_choose_fuzz() function rather than polluting runq_choose()
with 4BSD specific code.
- Move the fuzz sysctl into sched_4bsd.c
- Remove some dead code from kern_switch.c
requiring the per-process spinlock to only requiring the process lock.
- Reflect these changes in the proc.h documentation and consumers throughout
the kernel. This is a substantial reduction in locking cost for these
fields and was made possible by recent changes to threading support.
after each SYSINIT() macro invocation. This makes a number of
lightweight C parsers much happier with the FreeBSD kernel
source, including cflow's prcc and lxr.
MFC after: 1 month
Discussed with: imp, rink
While the KSE project was quite successful in bringing threading to
FreeBSD, the M:N approach taken by the kse library was never developed
to its full potential. Backwards compatibility will be provided via
libmap.conf for dynamically linked binaries and static binaries will
be broken.
sched_sleep(). This removes extra thread_lock() acquisition and
allows the scheduler to decide what to do with the static boost.
- Change the priority arguments to cv_* to match sleepq/msleep/etc.
where 0 means no priority change. Catch -1 in cv_broadcastpri() and
convert it to 0 for now.
- Set a flag when sleeping in a way that is compatible with swapping
since direct priority comparisons are meaningless now.
- Add a sysctl to ule, kern.sched.static_boost, that defaults to on which
controls the boost behavior. Turning it off gives better performance
in some workloads but needs more investigation.
- While we're modifying sleepq, change signal and broadcast to both
return with the lock held as the lock was held on enter.
Reviewed by: jhb, peter
the ABI when enabled. There is no longer an embedded lock_profile_object
in each lock. Instead a list of lock_profile_objects is kept per-thread
for each lock it may own. The cnt_hold statistic is now always 0 to
facilitate this.
- Support shared locking by tracking individual lock instances and
statistics in the per-thread per-instance lock_profile_object.
- Make the lock profiling hash table a per-cpu singly linked list with a
per-cpu static lock_prof allocator. This removes the need for an array
of spinlocks and reduces cache contention between cores.
- Use a seperate hash for spinlocks and other locks so that only a
critical_enter() is required and not a spinlock_enter() to modify the
per-cpu tables.
- Count time spent spinning in the lock statistics.
- Remove the LOCK_PROFILE_SHARED option as it is always supported now.
- Specifically drop and release the scheduler locks in both schedulers
since we track owners now.
In collaboration with: Kip Macy
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.
userland preemption directly from hardclock() via sched_clock() when a
thread uses up a full quantum instead of using a periodic timeout to cause
a userland preemption every so often. This fixes a potential deadlock
when IPI_PREEMPTION isn't enabled where softclock blocks on a lock held
by a thread pinned or bound to another CPU. The current thread on that
CPU will never be preempted while softclock is blocked.
Note that ULE already drives its round-robin userland preemption from
sched_clock() as well and always enables IPI_PREEMPT.
MFC after: 1 week
kthread_add() takes the same parameters as the old kthread_create()
plus a pointer to a process structure, and adds a kernel thread
to that process.
kproc_kthread_add() takes the parameters for kthread_add,
plus a process name and a pointer to a pointer to a process instead of just
a pointer, and if the proc * is NULL, it creates the process to the
specifications required, before adding the thread to it.
All other old kthread_xxx() calls return, but act on (struct thread *)
instead of (struct proc *). One reason to change the name is so that
any old kernel modules that are lying around and expect kthread_create()
to make a process will not just accidentally link.
fix top to show kernel threads by their thread name in -SH mode
add a tdnam formatting option to ps to show thread names.
make all idle threads actual kthreads and put them into their own idled process.
make all interrupt threads kthreads and put them in an interd process
(mainly for aesthetic and accounting reasons)
rename proc 0 to be 'kernel' and it's swapper thread is now 'swapper'
man page fixes to follow.
to simply switch rather than lowering priority and switching. This allows
threads of equal priority to run but not lesser priority.
Discussed with: davidxu
Reported by: NIIMI Satoshi <sa2c@sa2c.net>
Approved by: re
changes the units from seconds to the value of 'ticks' when swapped
in/out. ULE does not have a periodic timer that scans all threads in
the system and as such maintaining a per-second counter is difficult.
- Change computations requiring the unit in seconds to subtract ticks
and divide by hz. This does make the wraparound condition hz times
more frequent but this is still in the range of several months to
years and the adverse effects are minimal.
Approved by: re
- p_sflag was mostly protected by PROC_LOCK rather than the PROC_SLOCK or
previously the sched_lock. These bugs have existed for some time.
- Allow swapout to try each thread in a process individually and then
swapin the whole process if any of these fail. This allows us to move
most scheduler related swap flags into td_flags.
- Keep ki_sflag for backwards compat but change all in source tools to
use the new and more correct location of P_INMEM.
Reported by: pho
Reviewed by: attilio, kib
Approved by: re (kensmith)
new code and third party modules which try to depend on it.
- Initialize sched_lock in sched_4bsd.c.
- Declare sched_lock in sparc64 pmap.c and assert that we're compiling
with SCHED_4BSD to prevent accidental crashes from running ULE. This
is the sole remaining file outside of the scheduler that uses the
global sched_lock.
Approved by: re
- 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)
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}.
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.
