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| author | Andriy Gapon <avg@FreeBSD.org> | 2017-01-19 18:46:41 +0000 |
|---|---|---|
| committer | Andriy Gapon <avg@FreeBSD.org> | 2017-01-19 18:46:41 +0000 |
| commit | ad9dadc437ff470f794ce2fd0cd1714d69d725d3 (patch) | |
| tree | f7bc2af646648bba4dd9de30d47ac88d537c4783 /sys/kern | |
| parent | 1c07d69bc22d7176d38cdb71201f282578fc7391 (diff) | |
| download | src-ad9dadc437ff470f794ce2fd0cd1714d69d725d3.tar.gz src-ad9dadc437ff470f794ce2fd0cd1714d69d725d3.zip | |
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
Notes
Notes:
svn path=/head/; revision=312426
Diffstat (limited to 'sys/kern')
| -rw-r--r-- | sys/kern/sched_4bsd.c | 4 | ||||
| -rw-r--r-- | sys/kern/sched_ule.c | 4 |
2 files changed, 4 insertions, 4 deletions
diff --git a/sys/kern/sched_4bsd.c b/sys/kern/sched_4bsd.c index f97da1714681..534f59cd5a42 100644 --- a/sys/kern/sched_4bsd.c +++ b/sys/kern/sched_4bsd.c @@ -968,8 +968,8 @@ sched_switch(struct thread *td, struct thread *newtd, int flags) sched_load_rem(); td->td_lastcpu = td->td_oncpu; - preempted = !((td->td_flags & TDF_SLICEEND) || - (flags & SWT_RELINQUISH)); + preempted = (td->td_flags & TDF_SLICEEND) == 0 && + (flags & SW_PREEMPT) != 0; td->td_flags &= ~(TDF_NEEDRESCHED | TDF_SLICEEND); td->td_owepreempt = 0; td->td_oncpu = NOCPU; diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c index 8bbd70952751..b650f24db9e5 100644 --- a/sys/kern/sched_ule.c +++ b/sys/kern/sched_ule.c @@ -1898,8 +1898,8 @@ sched_switch(struct thread *td, struct thread *newtd, int flags) ts->ts_rltick = ticks; td->td_lastcpu = td->td_oncpu; td->td_oncpu = NOCPU; - preempted = !((td->td_flags & TDF_SLICEEND) || - (flags & SWT_RELINQUISH)); + preempted = (td->td_flags & TDF_SLICEEND) == 0 && + (flags & SW_PREEMPT) != 0; td->td_flags &= ~(TDF_NEEDRESCHED | TDF_SLICEEND); td->td_owepreempt = 0; if (!TD_IS_IDLETHREAD(td)) |