Author: avg Date: Thu Jan 19 18:46:41 2017 New Revision: 312426 URL: https://svnweb.freebsd.org/changeset/base/312426
Log: 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 Modified: head/sys/kern/sched_4bsd.c head/sys/kern/sched_ule.c Modified: head/sys/kern/sched_4bsd.c ============================================================================== --- head/sys/kern/sched_4bsd.c Thu Jan 19 18:38:58 2017 (r312425) +++ head/sys/kern/sched_4bsd.c Thu Jan 19 18:46:41 2017 (r312426) @@ -968,8 +968,8 @@ sched_switch(struct thread *td, struct t 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; Modified: head/sys/kern/sched_ule.c ============================================================================== --- head/sys/kern/sched_ule.c Thu Jan 19 18:38:58 2017 (r312425) +++ head/sys/kern/sched_ule.c Thu Jan 19 18:46:41 2017 (r312426) @@ -1898,8 +1898,8 @@ sched_switch(struct thread *td, struct t 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)) _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
