81 lines
2.9 KiB
Diff
81 lines
2.9 KiB
Diff
From f089c645b517d22f97433deffaaedc9fd6f9b598 Mon Sep 17 00:00:00 2001
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From: Frederic Weisbecker <frederic@kernel.org>
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Date: Tue, 5 Apr 2022 03:07:51 +0200
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Subject: [PATCH 020/195] rcutorture: Also force sched priority to timersd on
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boosting test.
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ksoftirqd is statically boosted to the priority level right above the
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one of rcu_torture_boost() so that timers, which torture readers rely on,
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get a chance to run while rcu_torture_boost() is polling.
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However timers processing got split from ksoftirqd into their own kthread
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(timersd) that isn't boosted. It has the same SCHED_FIFO low prio as
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rcu_torture_boost() and therefore timers can't preempt it and may
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starve.
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The issue can be triggered in practice on v5.17.1-rt17 using:
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./kvm.sh --allcpus --configs TREE04 --duration 10m --kconfig "CONFIG_EXPERT=y CONFIG_PREEMPT_RT=y"
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Fix this with statically boosting timersd just like is done with
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ksoftirqd in commit
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ea6d962e80b61 ("rcutorture: Judge RCU priority boosting on grace periods, not callbacks")
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Suggested-by: Mel Gorman <mgorman@suse.de>
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Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Cc: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
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Link: https://lkml.kernel.org/r/20220405010752.1347437-1-frederic@kernel.org
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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include/linux/interrupt.h | 1 +
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kernel/rcu/rcutorture.c | 6 ++++++
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kernel/softirq.c | 2 +-
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3 files changed, 8 insertions(+), 1 deletion(-)
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diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
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index 0efba74a835c..f459b0f27c94 100644
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--- a/include/linux/interrupt.h
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+++ b/include/linux/interrupt.h
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@@ -610,6 +610,7 @@ extern void raise_softirq_irqoff(unsigned int nr);
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extern void raise_softirq(unsigned int nr);
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#ifdef CONFIG_PREEMPT_RT
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+DECLARE_PER_CPU(struct task_struct *, timersd);
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extern void raise_timer_softirq(void);
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extern void raise_hrtimer_softirq(void);
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diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
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index ade42d6a9d9b..eebb9b4548fb 100644
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--- a/kernel/rcu/rcutorture.c
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+++ b/kernel/rcu/rcutorture.c
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@@ -2408,6 +2408,12 @@ static int rcutorture_booster_init(unsigned int cpu)
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WARN_ON_ONCE(!t);
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sp.sched_priority = 2;
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sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
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+#ifdef CONFIG_PREEMPT_RT
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+ t = per_cpu(timersd, cpu);
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+ WARN_ON_ONCE(!t);
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+ sp.sched_priority = 2;
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+ sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
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+#endif
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}
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/* Don't allow time recalculation while creating a new task. */
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diff --git a/kernel/softirq.c b/kernel/softirq.c
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index c29c30106eb8..1277abc94228 100644
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--- a/kernel/softirq.c
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+++ b/kernel/softirq.c
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@@ -620,7 +620,7 @@ static inline void tick_irq_exit(void)
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}
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#ifdef CONFIG_PREEMPT_RT
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-static DEFINE_PER_CPU(struct task_struct *, timersd);
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+DEFINE_PER_CPU(struct task_struct *, timersd);
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static DEFINE_PER_CPU(unsigned long, pending_timer_softirq);
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static unsigned int local_pending_timers(void)
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--
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2.43.0
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