From owner-svn-src-all@freebsd.org Thu Feb 16 20:31:52 2017 Return-Path: Delivered-To: svn-src-all@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id CCDF6CE2370; Thu, 16 Feb 2017 20:31:52 +0000 (UTC) (envelope-from cy.schubert@komquats.com) Received: from smtp-out-so.shaw.ca (smtp-out-so.shaw.ca [64.59.136.139]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "Client", Issuer "CA" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id 674EA1D19; Thu, 16 Feb 2017 20:31:51 +0000 (UTC) (envelope-from cy.schubert@komquats.com) Received: from spqr.komquats.com ([96.50.22.10]) by shaw.ca with SMTP id eSiTc3UFKsa1keSiUcVcoi; Thu, 16 Feb 2017 13:31:51 -0700 X-Authority-Analysis: v=2.2 cv=W+NIbVek c=1 sm=1 tr=0 a=jvE2nwUzI0ECrNeyr98KWA==:117 a=jvE2nwUzI0ECrNeyr98KWA==:17 a=kj9zAlcOel0A:10 a=n2v9WMKugxEA:10 a=6I5d2MoRAAAA:8 a=YxBL1-UpAAAA:8 a=j9e7v2RgpAP0KFEN9twA:9 a=wFytJBbQj98qeGYh:21 a=DJLbta-Kyx7JE-Rh:21 a=CjuIK1q_8ugA:10 a=IjZwj45LgO3ly-622nXo:22 a=Ia-lj3WSrqcvXOmTRaiG:22 Received: from slippy.cwsent.com (slippy8 [10.2.2.6]) by spqr.komquats.com (Postfix) with ESMTPS id 90101DA1; Thu, 16 Feb 2017 12:31:49 -0800 (PST) Received: from slippy (localhost [127.0.0.1]) by slippy.cwsent.com (8.15.2/8.15.2) with ESMTP id v1GKVmjA097376; Thu, 16 Feb 2017 12:31:48 -0800 (PST) (envelope-from Cy.Schubert@cschubert.com) Message-Id: <201702162031.v1GKVmjA097376@slippy.cwsent.com> X-Mailer: exmh version 2.8.0 04/21/2012 with nmh-1.6 Reply-to: Cy Schubert From: Cy Schubert X-os: FreeBSD X-Sender: cy@cwsent.com X-URL: http://www.cschubert.com/ To: Ryan Stone cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r313814 - head/sys/kern In-Reply-To: Message from Ryan Stone of "Thu, 16 Feb 2017 19:41:13 +0000." <201702161941.v1GJfDoP087457@repo.freebsd.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Thu, 16 Feb 2017 12:31:48 -0800 X-CMAE-Envelope: MS4wfKwUkmMUj32K8SmJbKX8rL3H1V895iGE4ZxYIRKPQCxIVa0oZU4VLODgyYIGEan845kJG1wbwxZuDJTYzJkcl0meWityk21dOW5B+EmDKPJlWTlLLlrl dEKbxicm4GHswdm++Dae12nZjpOhWU4BNP07VWn1hSKaXM0Tc9PT4+I73Xfg1KiO3/klgx188Dj6samQ5Gyl57l6SSzixG9BHeWXT6fSlBwPl5AeqMXawx5X PDPFxGKoJoHyWTaOLWNNrEHGnhaCxo9ikSwwAvS5A8+DMKv32jnwF+FutHnnk/iI X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 16 Feb 2017 20:31:52 -0000 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 FreeBSD UNIX: 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 > >