fix a thread preemption regression in schedulers introduced in r270423

Commit r270423 fixed a regression in sched_yield() that was introduced
in earlier changes. Unfortunately, at the same time it

fix a thread preemption regression in schedulers introduced in r270423

Commit r270423 fixed a regression in sched_yield() that was introduced
in earlier changes. Unfortunately, at the same time it introduced an
new regression. The problem is that SWT_RELINQUISH (6), like all other
SWT_* constants and unlike SW_* flags, is not a bit flag. So, (flags &
SWT_RELINQUISH) is true in cases where that was not really indended,
for example, with SWT_OWEPREEMPT (2) and SWT_REMOTEPREEMPT (11).

A straight forward fix would be to use (flags & SW_TYPE_MASK) ==
SWT_RELINQUISH, but my impression is that the switch types are designed
mostly for gathering statistics, not for influencing scheduling
decisions.

So, I decided that it would be better to check for SW_PREEMPT flag
instead. That's also the same flag that was checked before r239157.
I double-checked how that flag is used and I am confident that the flag
is set only in the places where we really have the preemption:
- critical_exit + td_owepreempt
- sched_preempt in the ULE scheduler
- sched_preempt in the 4BSD scheduler

Reviewed by: kib, mav
MFC after: 4 days
Sponsored by: Panzura
Differential Revision: https://reviews.freebsd.org/D9230

show more ...

Merge ^/head r308491 through r308841.

Allow scheduling during early boot.

- Send IPI wakeups once SMP is started even if cold is true.
- Permit preemptions when cold is true.

These changes are needed for EARLY_AP_STARTUP.

MFC after: 2

Allow scheduling during early boot.

- Send IPI wakeups once SMP is started even if cold is true.
- Permit preemptions when cold is true.

These changes are needed for EARLY_AP_STARTUP.

MFC after: 2 weeks
Sponsored by: Netflix

show more ...

Don't place threads on the run queue after waking up other CPUs.

The other CPU might resume and see a still-empty runq and go back to
sleep before sched_add() adds the thread to the runq. This resu

Don't place threads on the run queue after waking up other CPUs.

The other CPU might resume and see a still-empty runq and go back to
sleep before sched_add() adds the thread to the runq. This results
in a lost wakeup and a potential hang if the system is otherwise
completely idle.

The race originated due to a micro-optimization (my fault) in 4BSD in
that it avoided putting a thread on the run queue if the scheduler was
going to preempt to the new thread. To avoid complexity while fixing
this race, just drop this optimization. 4BSD now always sets the
"owepreempt" flag when a preemption is warranted and defers the actual
preemption to the thread_unlock of the caller the same as ULE.

MFC after: 2 weeks
Sponsored by: Netflix

show more ...

Merge ^/head r305687 through r305890.

Renumber license clauses in sys/kern to avoid skipping #3

Merge ^/head r303250 through r304235.

Don't treat NOCPU as a valid CPU to CPU_ISSET.

If a thread is created bound to a cpuset it might already be bound before
it's very first timeslice, and td_lastcpu will be NOCPU in that case.

MFC af

Don't treat NOCPU as a valid CPU to CPU_ISSET.

If a thread is created bound to a cpuset it might already be bound before
it's very first timeslice, and td_lastcpu will be NOCPU in that case.

MFC after: 1 week

show more ...

Get rid of struct proc p_sched and struct thread td_sched pointers.

p_sched is unused.

The struct td_sched is always co-allocated with the struct thread,
except for the thread0. Avoid useless indi

Get rid of struct proc p_sched and struct thread td_sched pointers.

p_sched is unused.

The struct td_sched is always co-allocated with the struct thread,
except for the thread0. Avoid useless indirection, instead calculate
td_sched location using simple pointer arithmetic in td_get_sched(9).
For thread0, which is statically allocated, create a structure to
emulate layout of the dynamic allocation.

Reviewed by: jhb (previous version)
Sponsored by: The FreeBSD Foundation
Differential revision: https://reviews.freebsd.org/D6711

show more ...

sys/kern: spelling fixes in comments.

No functional change.

The struct thread td_estcpu member is only used by the 4BSD scheduler.
Move it to the struct td_sched for 4BSD, removing always present
field, otherwise unused for ULE.

New scheduler method sched_es

The struct thread td_estcpu member is only used by the 4BSD scheduler.
Move it to the struct td_sched for 4BSD, removing always present
field, otherwise unused for ULE.

New scheduler method sched_estcpu() returns the estimation for
kinfo_proc consumption. As before, it always returns 0 for ULE.

Remove sched_tick() scheduler method, unused both by 4BSD and ULE.

Update locking comment for the 4BSD struct td_sched, copying it from
the same comment for ULE.

Spell MAXPRI as PRI_MAX_TIMESHARE in the 4BSD comment.

Based on some notes from, and reviewed by: bde
Sponsored by: The FreeBSD Foundation

show more ...

Merge from head

Sponsored by: Gandi.net

Finish merging from head, messed up in previous attempt

Catch up with head, primarily for the 1.14.4.0 firmware.

Merge ^/head r285924 through r286421.

kgdb uses td_oncpu to determine if a thread is running and should use
a pcb from stoppcbs[] rather than the thread's PCB. However, exited threads
retained td_oncpu from the last time they ran, and n

kgdb uses td_oncpu to determine if a thread is running and should use
a pcb from stoppcbs[] rather than the thread's PCB. However, exited threads
retained td_oncpu from the last time they ran, and newborn threads had their
CPU fields cleared to zero during fork and thread creation since they are
in the set of fields zeroed when threads are setup. To fix, explicitly
update the CPU fields for exiting threads in sched_throw() to reflect the
switch out and reset the CPU fields for new threads in sched_fork_thread()
to NOCPU.

Reviewed by: kib
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D3193

show more ...

Catch up with HEAD (r280229-r284686).

Merge sync of head

Merge from head

MFH: r281855-r282312

Sponsored by: The FreeBSD Foundation

Add kern.racct.enable tunable and RACCT_DISABLED config option.
The point of this is to be able to add RACCT (with RACCT_DISABLED)
to GENERIC, to avoid having to rebuild the kernel to use rctl(8).

D

Add kern.racct.enable tunable and RACCT_DISABLED config option.
The point of this is to be able to add RACCT (with RACCT_DISABLED)
to GENERIC, to avoid having to rebuild the kernel to use rctl(8).

Differential Revision: https://reviews.freebsd.org/D2369
Reviewed by: kib@
MFC after: 1 month
Relnotes: yes
Sponsored by: The FreeBSD Foundation

show more ...

Merge from head@274682

IFC @r271694

Sync to HEAD@r271160.

Restore pre-r239157 handling of sched_yield(), when thread time slice was
aborted, allowing other threads to run. Without this change thread is just
rescheduled again, that was illustrated by provid

Restore pre-r239157 handling of sched_yield(), when thread time slice was
aborted, allowing other threads to run. Without this change thread is just
rescheduled again, that was illustrated by provided test tool.

PR: 192926
Submitted by: eric@vangyzen.net
MFC after: 2 weeks

show more ...