svn commit: r313814 - head/sys/kern
O. Hartmann
ohartmann at walstatt.org
Thu Feb 16 19:55:20 UTC 2017
Am Thu, 16 Feb 2017 19:41:13 +0000 (UTC)
Ryan Stone <rstone at 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
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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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