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[192.222.189.155]) by smtp.gmail.com with ESMTPSA id r34sm150885qtr.18.2020.08.28.12.52.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Aug 2020 12:52:43 -0700 (PDT) From: Julien Desfossez To: Peter Zijlstra , Vineeth Pillai , Joel Fernandes , Tim Chen , Aaron Lu , Aubrey Li , Dhaval Giani , Chris Hyser , Nishanth Aravamudan Cc: mingo@kernel.org, tglx@linutronix.de, pjt@google.com, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com, Phil Auld , Valentin Schneider , Mel Gorman , Pawan Gupta , Paolo Bonzini , joel@joelfernandes.org, vineeth@bitbyteword.org, Chen Yu , Christian Brauner , Agata Gruza , Antonio Gomez Iglesias , graf@amazon.com, konrad.wilk@oracle.com, dfaggioli@suse.com, rostedt@goodmis.org, derkling@google.com, benbjiang@tencent.com Subject: [RFC PATCH v7 12/23] sched: Trivial forced-newidle balancer Date: Fri, 28 Aug 2020 15:51:13 -0400 Message-Id: X-Mailer: git-send-email 2.17.1 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra When a sibling is forced-idle to match the core-cookie; search for matching tasks to fill the core. rcu_read_unlock() can incur an infrequent deadlock in sched_core_balance(). Fix this by using the RCU-sched flavor instead. Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Joel Fernandes (Google) Acked-by: Paul E. McKenney --- include/linux/sched.h | 1 + kernel/sched/core.c | 130 +++++++++++++++++++++++++++++++++++++++++- kernel/sched/idle.c | 1 + kernel/sched/sched.h | 6 ++ 4 files changed, 137 insertions(+), 1 deletion(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 5fe9878502cb..eee53fa7b8d4 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -687,6 +687,7 @@ struct task_struct { #ifdef CONFIG_SCHED_CORE struct rb_node core_node; unsigned long core_cookie; + unsigned int core_occupation; #endif #ifdef CONFIG_CGROUP_SCHED diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 707a56ef0fa3..7e2f310ec0c0 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -201,6 +201,21 @@ static struct task_struct *sched_core_find(struct rq *rq, unsigned long cookie) return match; } +static struct task_struct *sched_core_next(struct task_struct *p, unsigned long cookie) +{ + struct rb_node *node = &p->core_node; + + node = rb_next(node); + if (!node) + return NULL; + + p = container_of(node, struct task_struct, core_node); + if (p->core_cookie != cookie) + return NULL; + + return p; +} + /* * The static-key + stop-machine variable are needed such that: * @@ -4641,7 +4656,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) struct task_struct *next, *max = NULL; const struct sched_class *class; const struct cpumask *smt_mask; - int i, j, cpu; + int i, j, cpu, occ = 0; int smt_weight; bool need_sync; @@ -4750,6 +4765,9 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) goto done; } + if (!is_idle_task(p)) + occ++; + rq_i->core_pick = p; /* @@ -4775,6 +4793,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) cpu_rq(j)->core_pick = NULL; } + occ = 1; goto again; } else { /* @@ -4820,6 +4839,8 @@ next_class:; if (is_idle_task(rq_i->core_pick) && rq_i->nr_running) rq_i->core_forceidle = true; + rq_i->core_pick->core_occupation = occ; + if (i == cpu) continue; @@ -4837,6 +4858,113 @@ next_class:; return next; } +static bool try_steal_cookie(int this, int that) +{ + struct rq *dst = cpu_rq(this), *src = cpu_rq(that); + struct task_struct *p; + unsigned long cookie; + bool success = false; + + local_irq_disable(); + double_rq_lock(dst, src); + + cookie = dst->core->core_cookie; + if (!cookie) + goto unlock; + + if (dst->curr != dst->idle) + goto unlock; + + p = sched_core_find(src, cookie); + if (p == src->idle) + goto unlock; + + do { + if (p == src->core_pick || p == src->curr) + goto next; + + if (!cpumask_test_cpu(this, &p->cpus_mask)) + goto next; + + if (p->core_occupation > dst->idle->core_occupation) + goto next; + + p->on_rq = TASK_ON_RQ_MIGRATING; + deactivate_task(src, p, 0); + set_task_cpu(p, this); + activate_task(dst, p, 0); + p->on_rq = TASK_ON_RQ_QUEUED; + + resched_curr(dst); + + success = true; + break; + +next: + p = sched_core_next(p, cookie); + } while (p); + +unlock: + double_rq_unlock(dst, src); + local_irq_enable(); + + return success; +} + +static bool steal_cookie_task(int cpu, struct sched_domain *sd) +{ + int i; + + for_each_cpu_wrap(i, sched_domain_span(sd), cpu) { + if (i == cpu) + continue; + + if (need_resched()) + break; + + if (try_steal_cookie(cpu, i)) + return true; + } + + return false; +} + +static void sched_core_balance(struct rq *rq) +{ + struct sched_domain *sd; + int cpu = cpu_of(rq); + + preempt_disable(); + rcu_read_lock(); + raw_spin_unlock_irq(rq_lockp(rq)); + for_each_domain(cpu, sd) { + if (need_resched()) + break; + + if (steal_cookie_task(cpu, sd)) + break; + } + raw_spin_lock_irq(rq_lockp(rq)); + rcu_read_unlock(); + preempt_enable(); +} + +static DEFINE_PER_CPU(struct callback_head, core_balance_head); + +void queue_core_balance(struct rq *rq) +{ + if (!sched_core_enabled(rq)) + return; + + if (!rq->core->core_cookie) + return; + + if (!rq->nr_running) /* not forced idle */ + return; + + queue_balance_callback(rq, &per_cpu(core_balance_head, rq->cpu), sched_core_balance); +} + #else /* !CONFIG_SCHED_CORE */ static struct task_struct * diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 8c41b023dd14..9c5637d866fd 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -406,6 +406,7 @@ static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool fir { update_idle_core(rq); schedstat_inc(rq->sched_goidle); + queue_core_balance(rq); } #ifdef CONFIG_SMP diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 7e9346de3f59..be6db45276e7 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1109,6 +1109,8 @@ static inline raw_spinlock_t *rq_lockp(struct rq *rq) bool cfs_prio_less(struct task_struct *a, struct task_struct *b); void sched_core_adjust_sibling_vruntime(int cpu, bool coresched_enabled); +extern void queue_core_balance(struct rq *rq); + #else /* !CONFIG_SCHED_CORE */ static inline bool sched_core_enabled(struct rq *rq) @@ -1121,6 +1123,10 @@ static inline raw_spinlock_t *rq_lockp(struct rq *rq) return &rq->__lock; } +static inline void queue_core_balance(struct rq *rq) +{ +} + #endif /* CONFIG_SCHED_CORE */ #ifdef CONFIG_SCHED_SMT -- 2.17.1