Am Thu, 16 Feb 2017 19:41:13 +0000 (UTC) Ryan Stone <rst...@freebsd.org> schrieb:
> Author: rstone > Date: Thu Feb 16 19:41:13 2017 > New Revision: 313814 > URL: https://svnweb.freebsd.org/changeset/base/313814 > > Log: > Check for preemption after lowering a thread's priority > > When a high-priority thread is waiting for a mutex held by a > low-priority thread, it temporarily lends its priority to the > low-priority thread to prevent priority inversion. When the mutex > is released, the lent priority is revoked and the low-priority > thread goes back to its original priority. > > When the priority of that thread is lowered (through a call to > sched_priority()), the schedule was not checking whether > there is now a high-priority thread in the run queue. This can > cause threads with real-time priority to be starved in the run > queue while the low-priority thread finishes its quantum. > > Fix this by explicitly checking whether preemption is necessary > when a thread's priority is lowered. > > Sponsored by: Dell EMC Isilon > Obtained from: Sandvine Inc > Differential Revision: https://reviews.freebsd.org/D9518 > Reviewed by: Jeff Roberson (ule) > MFC after: 1 month > > 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 Feb 16 19:00:09 2017 > (r313813) > +++ head/sys/kern/sched_4bsd.c Thu Feb 16 19:41:13 2017 > (r313814) > @@ -816,7 +816,12 @@ sched_class(struct thread *td, int class > static void > sched_priority(struct thread *td, u_char prio) > { > - > + struct thread *newtd; > + struct runq *rq; > + u_char orig_pri; > +#ifdef SMP > + struct thread *cputd; > +#endif > > KTR_POINT3(KTR_SCHED, "thread", sched_tdname(td), "priority change", > "prio:%d", td->td_priority, "new prio:%d", prio, KTR_ATTR_LINKED, > @@ -832,10 +837,43 @@ sched_priority(struct thread *td, u_char > THREAD_LOCK_ASSERT(td, MA_OWNED); > if (td->td_priority == prio) > return; > + orig_pri = td->td_priority; > td->td_priority = prio; > if (TD_ON_RUNQ(td) && td->td_rqindex != (prio / RQ_PPQ)) { > sched_rem(td); > sched_add(td, SRQ_BORING); > + } else if (orig_pri < prio && TD_IS_RUNNING(td)) { > + /* > + * If we have decreased the priority of a running thread, we > + * have to check if it should be preempted. > + */ > + rq = &runq; > + newtd = runq_choose(&runq); > +#ifdef SMP > + cputd = runq_choose(&runq_pcpu[td->td_oncpu]); > + if (newtd == NULL || > + (cputd != NULL && cputd->td_priority < td->td_priority)) > + newtd = cputd; > +#endif > + > + if (newtd != NULL && newtd->td_priority < prio > +#ifndef FULL_PREEMPTION > + && (newtd->td_priority <= PRI_MAX_ITHD || > + prio >= PRI_MIN_IDLE)) > +#endif > + ) { > + if (td == curthread) > + /* > + * Don't reschedule the thread here as it may > + * be losing priority because it has released a > + * mutex, and in that case we need it to finish > + * releasing the lock before it gets preempted. > + */ > + td->td_owepreempt = 1; > + else > + kick_other_cpu(newtd->td_priority, > + td->td_oncpu); > + } > } > } > > > Modified: head/sys/kern/sched_ule.c > ============================================================================== > --- head/sys/kern/sched_ule.c Thu Feb 16 19:00:09 2017 (r313813) > +++ head/sys/kern/sched_ule.c Thu Feb 16 19:41:13 2017 (r313814) > @@ -319,7 +319,7 @@ static void tdq_add(struct tdq *, struct > #ifdef SMP > static int tdq_move(struct tdq *, struct tdq *); > static int tdq_idled(struct tdq *); > -static void tdq_notify(struct tdq *, struct thread *); > +static void tdq_notify(struct tdq *, int); > static struct thread *tdq_steal(struct tdq *, int); > static struct thread *runq_steal(struct runq *, int); > static int sched_pickcpu(struct thread *, int); > @@ -1040,16 +1040,14 @@ tdq_idled(struct tdq *tdq) > * Notify a remote cpu of new work. Sends an IPI if criteria are met. > */ > static void > -tdq_notify(struct tdq *tdq, struct thread *td) > +tdq_notify(struct tdq *tdq, int pri) > { > struct thread *ctd; > - int pri; > int cpu; > > if (tdq->tdq_ipipending) > return; > - cpu = td_get_sched(td)->ts_cpu; > - pri = td->td_priority; > + cpu = TD_ID(tdq); > ctd = pcpu_find(cpu)->pc_curthread; > if (!sched_shouldpreempt(pri, ctd->td_priority, 1)) > return; > @@ -1675,6 +1673,22 @@ sched_pctcpu_update(struct td_sched *ts, > ts->ts_ltick = t; > } > > +static void > +sched_check_preempt(struct tdq *tdq, struct thread *td) > +{ > + > + KASSERT(TD_IS_RUNNING(td), ("thread is not running")); > + TDQ_LOCK_ASSERT(tdq, MA_OWNED); > + KASSERT(tdq == TDQ_CPU(td->td_sched->ts_cpu), > + ("tdq does not contain td")); > + > + if (tdq == TDQ_SELF()) { > + if (sched_shouldpreempt(tdq->tdq_lowpri, td->td_priority, 0)) > + td->td_owepreempt = 1; > + } else > + tdq_notify(tdq, tdq->tdq_lowpri); > +} > + > /* > * Adjust the priority of a thread. Move it to the appropriate run-queue > * if necessary. This is the back-end for several priority related > @@ -1726,6 +1740,9 @@ sched_thread_priority(struct thread *td, > tdq->tdq_lowpri = prio; > else if (tdq->tdq_lowpri == oldpri) > tdq_setlowpri(tdq, td); > + > + if (oldpri < prio) > + sched_check_preempt(tdq, td); > return; > } > td->td_priority = prio; > @@ -1854,7 +1871,7 @@ sched_switch_migrate(struct tdq *tdq, st > */ > tdq_lock_pair(tdn, tdq); > tdq_add(tdn, td, flags); > - tdq_notify(tdn, td); > + tdq_notify(tdn, td->td_priority); > TDQ_UNLOCK(tdn); > spinlock_exit(); > #endif > @@ -2429,7 +2446,7 @@ sched_add(struct thread *td, int flags) > tdq = sched_setcpu(td, cpu, flags); > tdq_add(tdq, td, flags); > if (cpu != PCPU_GET(cpuid)) { > - tdq_notify(tdq, td); > + tdq_notify(tdq, td->td_priority); > return; > } > #else > _______________________________________________ > svn-src-h...@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/svn-src-head > To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org" This commit breaks buildkernel: --- sched_ule.o --- /usr/src/sys/kern/sched_ule.c:1050:8: error: implicit declaration of function 'TD_ID' is invalid in C99 [-Werror,-Wimplicit-function-declaration] cpu = TD_ID(tdq); ^ 1 error generated. *** [sched_ule.o] Error code 1 -- O. Hartmann Ich widerspreche der Nutzung oder Übermittlung meiner Daten für Werbezwecke oder für die Markt- oder Meinungsforschung (§ 28 Abs. 4 BDSG).
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