From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753200AbeFAPwk (ORCPT ); Fri, 1 Jun 2018 11:52:40 -0400 Received: from mail-pl0-f65.google.com ([209.85.160.65]:36772 "EHLO mail-pl0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752019AbeFAPwg (ORCPT ); Fri, 1 Jun 2018 11:52:36 -0400 X-Google-Smtp-Source: ADUXVKKYr7RUoUjZIe6G6r+WMA3ykb34NayS3YZI7I+0/OWk0tje5+WC2kpkDWSNgVfmxVuPfFHkww== Date: Fri, 1 Jun 2018 08:52:35 -0700 From: Joel Fernandes To: Byungchul Park Cc: peterz@infradead.org, mingo@kernel.org, rostedt@goodmis.org, tglx@linutronix.de, raistlin@linux.it, linux-kernel@vger.kernel.org, juri.lelli@gmail.com, bristot@redhat.com, kernel-team@lge.com, kernel-team@android.com Subject: Re: [RESEND, v3, 2/2] sched/deadline: Initialize cp->elements[].cpu to an invalid value Message-ID: <20180601155235.GA66123@joelaf.mtv.corp.google.com> References: <1515392081-32320-2-git-send-email-byungchul.park@lge.com> <20180601061255.GA189147@joelaf.mtv.corp.google.com> <20180601061841.GA191514@joelaf.mtv.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 01, 2018 at 04:10:56PM +0900, Byungchul Park wrote: > > On Thu, May 31, 2018 at 11:12:55PM -0700, Joel Fernandes wrote: > > > On Mon, Jan 08, 2018 at 03:14:41PM +0900, byungchul park wrote: > > > > Currently, migrating tasks to cpu0 unconditionally happens when the > > > > heap is empty, since cp->elements[].cpu was initialized to 0(=cpu0). > > > > We have to distinguish between the empty case and cpu0 to avoid the > > > > unnecessary migrations. Therefore, it has to return an invalid value > > > > e.i. -1 in that case. > > > > > > > > Signed-off-by: Byungchul Park > > > > Acked-by: Steven Rostedt (VMware) > > > > Acked-by: Daniel Bristot de Oliveira > > > > --- > > > > kernel/sched/cpudeadline.c | 10 +++++++++- > > > > 1 file changed, 9 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c > > > > index 9f02035..bcf903f 100644 > > > > --- a/kernel/sched/cpudeadline.c > > > > +++ b/kernel/sched/cpudeadline.c > > > > @@ -138,6 +138,12 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p, > > > > int best_cpu = cpudl_maximum_cpu(cp); > > > > WARN_ON(best_cpu != -1 && !cpu_present(best_cpu)); > > > > + /* > > > > + * The heap tree is empty for now, just return. > > > > + */ > > > > + if (best_cpu == -1) > > > > + return 0; > > > > + > > > > if (cpumask_test_cpu(best_cpu, &p->cpus_allowed) && > > > > dl_time_before(dl_se->deadline, cpudl_maximum_dl(cp))) { > > > > if (later_mask) > > > > @@ -265,8 +271,10 @@ int cpudl_init(struct cpudl *cp) > > > > return -ENOMEM; > > > > } > > > > - for_each_possible_cpu(i) > > > > + for_each_possible_cpu(i) { > > > > + cp->elements[i].cpu = -1; > > > > cp->elements[i].idx = IDX_INVALID; > > > > > > Shouldn't you also set cp->elements[cpu].cpu to -1 in cpudl_clear (when you > > > set cp->elements[cpu].cpu to IDX_INVALID there)? > > > > I messed up my words, I meant : "when setting cp->elements[cpu].idx to > > IDX_INVALID there". Which means I need to call it a day :-) > > Ah.. I agree with you. It might be a problem when removing the last > element.. Then I think the following change should also be applied > additionally. Right? Yes. > --- > diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c > index 8d9562d..44d4c88 100644 > --- a/kernel/sched/cpudeadline.c > +++ b/kernel/sched/cpudeadline.c > @@ -172,12 +172,14 @@ void cpudl_clear(struct cpudl *cp, int cpu) > } else { > new_cpu = cp->elements[cp->size - 1].cpu; > cp->elements[old_idx].dl = cp->elements[cp->size - 1].dl; > - cp->elements[old_idx].cpu = new_cpu; > + cp->elements[old_idx].cpu = (new_cpu == cpu) ? -1 : new_cpu; > cp->size--; > - cp->elements[new_cpu].idx = old_idx; > cp->elements[cpu].idx = IDX_INVALID; > - cpudl_heapify(cp, old_idx); > > + if (new_cpu != cpu) { > + cp->elements[new_cpu].idx = old_idx; > + cpudl_heapify(cp, old_idx); > + } > cpumask_set_cpu(cpu, cp->free_cpus); This looks a bit confusing. How about the following? (untested) thanks, - Joel ---8<----------------------- diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c index 50316455ea66..741a97e58c05 100644 --- a/kernel/sched/cpudeadline.c +++ b/kernel/sched/cpudeadline.c @@ -129,6 +129,10 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p, } else { int best_cpu = cpudl_maximum(cp); + /* The max-heap is empty, just return. */ + if (best_cpu == -1) + return 0; + WARN_ON(best_cpu != -1 && !cpu_present(best_cpu)); if (cpumask_test_cpu(best_cpu, &p->cpus_allowed) && @@ -167,6 +171,12 @@ void cpudl_clear(struct cpudl *cp, int cpu) * This could happen if a rq_offline_dl is * called for a CPU without -dl tasks running. */ + } else if (cp->size == 1) { + /* Only one element in max-heap, clear it */ + cp->elements[0].cpu = -1; + cp->elements[cpu].idx = IDX_INVALID; + cp->size--; + cpumask_set_cpu(cpu, cp->free_cpus); } else { new_cpu = cp->elements[cp->size - 1].cpu; cp->elements[old_idx].dl = cp->elements[cp->size - 1].dl; @@ -262,6 +272,9 @@ int cpudl_init(struct cpudl *cp) for_each_possible_cpu(i) cp->elements[i].idx = IDX_INVALID; + /* Mark heap as initially empty */ + cp->elements[0].cpu = -1; + return 0; }