From 9babcd7929bc8967ae3bb6093f603b93c2f9958f Mon Sep 17 00:00:00 2001 From: Daniel Bristot de Oliveira Date: Thu, 8 Oct 2015 15:36:06 -0300 Subject: [PATCH 1/6] sched, tracing: Stop/start critical timings around the idle=poll idle loop When using idle=poll, the preemptoff tracer is always showing the idle task as the culprit for long latencies. That happens because critical timings are not stopped before idle loop. This patch stops critical timings before entering the idle loop, starting it again after the idle loop. This problem does not affect the irqsoff tracer because interruptions are enabled before entering the idle loop. Signed-off-by: Daniel Bristot de Oliveira Reviewed-by: Luis Claudio R. Goncalves Acked-by: Steven Rostedt Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/10fc3705874aef11dbe152a068b591a7be1899b4.1444314899.git.bristot@redhat.com Signed-off-by: Ingo Molnar --- kernel/sched/idle.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 8f177c73ae19..4a2ef5a02fd3 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -57,9 +57,11 @@ static inline int cpu_idle_poll(void) rcu_idle_enter(); trace_cpu_idle_rcuidle(0, smp_processor_id()); local_irq_enable(); + stop_critical_timings(); while (!tif_need_resched() && (cpu_idle_force_poll || tick_check_broadcast_expired())) cpu_relax(); + start_critical_timings(); trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id()); rcu_idle_exit(); return 1; From fde7d22e01aa0d252fc5c95fa11f0dac35a4dd59 Mon Sep 17 00:00:00 2001 From: Yuyang Du Date: Tue, 13 Oct 2015 09:18:22 +0800 Subject: [PATCH 2/6] sched/fair: Fix overly small weight for interactive group entities Commit: 9d89c257dfb9 ("sched/fair: Rewrite runnable load and utilization average tracking") led to an overly small weight for interactive group entities. The bad case can be easily reproduced when a number of CPU hogs compete for the CPUs at the same time (thanks to Mike). This is largly because the task group's load average tracking cross CPUs lags behind the real changes. To fix this we accelerate the group share distribution process by using the load.weight of the cfs_rq. This may increase the entire group's share, but we have to do so to protect the (fragile) interactive tasks, especially from CPU hogs. Reported-by: Mike Galbraith Tested-by: Dietmar Eggemann Tested-by: Mike Galbraith Signed-off-by: Yuyang Du Signed-off-by: Peter Zijlstra (Intel) Acked-by: Dietmar Eggemann Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1444699103-20272-1-git-send-email-yuyang.du@intel.com Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 6e2e3483b1ec..bc62c5096e54 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2363,7 +2363,7 @@ static inline long calc_tg_weight(struct task_group *tg, struct cfs_rq *cfs_rq) */ tg_weight = atomic_long_read(&tg->load_avg); tg_weight -= cfs_rq->tg_load_avg_contrib; - tg_weight += cfs_rq_load_avg(cfs_rq); + tg_weight += cfs_rq->load.weight; return tg_weight; } @@ -2373,7 +2373,7 @@ static long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg) long tg_weight, load, shares; tg_weight = calc_tg_weight(tg, cfs_rq); - load = cfs_rq_load_avg(cfs_rq); + load = cfs_rq->load.weight; shares = (tg->shares * load); if (tg_weight) From 3e386d56bafbb6d2540b49367444997fc671ea69 Mon Sep 17 00:00:00 2001 From: Yuyang Du Date: Tue, 13 Oct 2015 09:18:23 +0800 Subject: [PATCH 3/6] sched/fair: Update task group's load_avg after task migration When cfs_rq has cfs_rq->removed_load_avg set (when a task migrates from this cfs_rq), we need to update its contribution to the group's load_avg. This should not increase tg's update too much, because in most cases, the cfs_rq has already decayed its load_avg. Tested-by: Dietmar Eggemann Signed-off-by: Yuyang Du Signed-off-by: Peter Zijlstra (Intel) Acked-by: Dietmar Eggemann Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1444699103-20272-2-git-send-email-yuyang.du@intel.com Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index bc62c5096e54..9a5e60fe721a 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2664,13 +2664,14 @@ static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq); /* Group cfs_rq's load_avg is used for task_h_load and update_cfs_share */ static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) { - int decayed; struct sched_avg *sa = &cfs_rq->avg; + int decayed, removed = 0; if (atomic_long_read(&cfs_rq->removed_load_avg)) { long r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0); sa->load_avg = max_t(long, sa->load_avg - r, 0); sa->load_sum = max_t(s64, sa->load_sum - r * LOAD_AVG_MAX, 0); + removed = 1; } if (atomic_long_read(&cfs_rq->removed_util_avg)) { @@ -2688,7 +2689,7 @@ static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) cfs_rq->load_last_update_time_copy = sa->last_update_time; #endif - return decayed; + return decayed || removed; } /* Update task and its cfs_rq load average */ From 0baabb385eb4bce699ddab0db015112be6cf1e6a Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Mon, 12 Oct 2015 17:21:23 +0200 Subject: [PATCH 4/6] nohz: Revert "nohz: Set isolcpus when nohz_full is set" This reverts: 8cb9764fc88b ("nohz: Set isolcpus when nohz_full is set") We assumed that full-nohz users always want scheduler isolation on full dynticks CPUs, therefore we included full-nohz CPUs on cpu_isolated_map. This means that tasks run by default on CPUs outside the nohz_full range unless their affinity is explicity overwritten. This suits pure isolation workloads but when the machine is needed to run common workloads, the available sets of CPUs to run common tasks becomes reduced. We reach an extreme case when CONFIG_NO_HZ_FULL_ALL is enabled as it leaves only CPU 0 for non-isolation tasks, which makes people think that their supercomputer regressed to 90's UP - which is true in a sense. Some full-nohz users appear to be interested in running normal workloads either before or after an isolation workload. Full-nohz isn't optimized toward normal workloads but it's still better than UP performance. We are reaching a limitation in kernel presets here. Lets revert this cpu_isolated_map inclusion and let userspace do its own scheduler isolation using cpusets or explicit affinity settings. Reported-by: Ingo Molnar Reported-by: Mike Galbraith Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Acked-by: Thomas Gleixner Cc: Alexey Dobriyan Cc: Andrew Morton Cc: Chris Metcalf Cc: Christoph Lameter Cc: Dave Jones Cc: Linus Torvalds Cc: Mike Galbraith Cc: Oleg Nesterov Cc: Paul E . McKenney Cc: Peter Zijlstra Cc: Rik van Riel Link: http://lkml.kernel.org/r/1444663283-30068-1-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 10a8faa1b0d4..5bd7d60658d3 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7238,9 +7238,6 @@ void __init sched_init_smp(void) alloc_cpumask_var(&non_isolated_cpus, GFP_KERNEL); alloc_cpumask_var(&fallback_doms, GFP_KERNEL); - /* nohz_full won't take effect without isolating the cpus. */ - tick_nohz_full_add_cpus_to(cpu_isolated_map); - sched_init_numa(); /* From 5aa5050787f449e7eaef2c5ec93c7b357aa7dcdc Mon Sep 17 00:00:00 2001 From: Luca Abeni Date: Fri, 16 Oct 2015 10:06:21 +0200 Subject: [PATCH 5/6] sched/deadline: Fix migration of SCHED_DEADLINE tasks Commit: 9d5142624256 ("sched/deadline: Reduce rq lock contention by eliminating locking of non-feasible target") broke select_task_rq_dl() and find_lock_later_rq(), because it introduced a comparison between the local task's deadline and dl.earliest_dl.curr of the remote queue. However, if the remote runqueue does not contain any SCHED_DEADLINE task its earliest_dl.curr is 0 (always smaller than the deadline of the local task) and the remote runqueue is not selected for pushing. As a result, if an application creates multiple SCHED_DEADLINE threads, they will never be pushed to runqueues that do not already contain SCHED_DEADLINE tasks. This patch fixes the issue by checking if dl.dl_nr_running == 0. Signed-off-by: Luca Abeni Signed-off-by: Peter Zijlstra (Intel) Cc: Juri Lelli Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Wanpeng Li Fixes: 9d5142624256 ("sched/deadline: Reduce rq lock contention by eliminating locking of non-feasible target") Link: http://lkml.kernel.org/r/1444982781-15608-1-git-send-email-luca.abeni@unitn.it Signed-off-by: Ingo Molnar --- kernel/sched/deadline.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index fc8f01083527..142df2668e5d 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -1066,8 +1066,9 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags) int target = find_later_rq(p); if (target != -1 && - dl_time_before(p->dl.deadline, - cpu_rq(target)->dl.earliest_dl.curr)) + (dl_time_before(p->dl.deadline, + cpu_rq(target)->dl.earliest_dl.curr) || + (cpu_rq(target)->dl.dl_nr_running == 0))) cpu = target; } rcu_read_unlock(); @@ -1417,7 +1418,8 @@ static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq) later_rq = cpu_rq(cpu); - if (!dl_time_before(task->dl.deadline, + if (later_rq->dl.dl_nr_running && + !dl_time_before(task->dl.deadline, later_rq->dl.earliest_dl.curr)) { /* * Target rq has tasks of equal or earlier deadline, From 0aaafaabfcba8aa991913cd3280a5dbf7f111a2a Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 23 Oct 2015 11:50:08 +0200 Subject: [PATCH 6/6] sched/core: Add missing lockdep_unpin() annotations Luca and Wanpeng reported two missing annotations that led to false lockdep complaints. Add the missing annotations. Reported-by: Luca Abeni Reported-by: Wanpeng Li Signed-off-by: Peter Zijlstra (Intel) Cc: Juri Lelli Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: cbce1a686700 ("sched,lockdep: Employ lock pinning") Link: http://lkml.kernel.org/r/20151023095008.GY17308@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 9 ++++++++- kernel/sched/deadline.c | 9 ++++++++- 2 files changed, 16 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 5bd7d60658d3..bcd214e4b4d6 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2366,8 +2366,15 @@ void wake_up_new_task(struct task_struct *p) trace_sched_wakeup_new(p); check_preempt_curr(rq, p, WF_FORK); #ifdef CONFIG_SMP - if (p->sched_class->task_woken) + if (p->sched_class->task_woken) { + /* + * Nothing relies on rq->lock after this, so its fine to + * drop it. + */ + lockdep_unpin_lock(&rq->lock); p->sched_class->task_woken(rq, p); + lockdep_pin_lock(&rq->lock); + } #endif task_rq_unlock(rq, p, &flags); } diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 142df2668e5d..8b0a15e285f9 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -668,8 +668,15 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer) * Queueing this task back might have overloaded rq, check if we need * to kick someone away. */ - if (has_pushable_dl_tasks(rq)) + if (has_pushable_dl_tasks(rq)) { + /* + * Nothing relies on rq->lock after this, so its safe to drop + * rq->lock. + */ + lockdep_unpin_lock(&rq->lock); push_dl_task(rq); + lockdep_pin_lock(&rq->lock); + } #endif unlock: