Date: Thu, 16 Feb 2017 15:37:54 -0500 From: Ryan Stone <rysto32@gmail.com> To: Cy Schubert <Cy.Schubert@komquats.com> Cc: Ryan Stone <rstone@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org> Subject: Re: svn commit: r313814 - head/sys/kern Message-ID: <CAFMmRNyuLTZ54TskavnJkssKwN94M-Sfb2VdGqj-2Zgs9tc=2g@mail.gmail.com> In-Reply-To: <201702162031.v1GKVmjA097376@slippy.cwsent.com> References: <rstone@FreeBSD.org> <201702161941.v1GJfDoP087457@repo.freebsd.org> <201702162031.v1GKVmjA097376@slippy.cwsent.com>
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Sorry about that. It's fixed in r313816. On Thu, Feb 16, 2017 at 3:31 PM, Cy Schubert <Cy.Schubert@komquats.com> wrote: > In message <201702161941.v1GJfDoP087457@repo.freebsd.org>, Ryan Stone > writes: > > 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 > (r31381 > > 3) > > +++ head/sys/kern/sched_4bsd.c Thu Feb 16 19:41:13 2017 > (r31381 > > 4) > > @@ -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); > > Just my luck. The day I svn up and rebuild. > > --- sched_ule.o --- > /opt/src/svn-current/sys/kern/sched_ule.c:1050:8: error: implicit > declaration of function 'TD_ID' is invalid in C99 > [-Werror,-Wimplicit-functi > on-declaration] > cpu = TD_ID(tdq); > ^ > -- > Cheers, > Cy Schubert <Cy.Schubert@cschubert.com> > FreeBSD UNIX: <cy@FreeBSD.org> Web: http://www.FreeBSD.org > > The need of the many outweighs the greed of the few. > > > > 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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