92 lines
2.5 KiB
Diff
92 lines
2.5 KiB
Diff
Subject: hotplug: Lightweight get online cpus
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From: Thomas Gleixner <tglx@linutronix.de>
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Date: Wed, 15 Jun 2011 12:36:06 +0200
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.1-rt3.tar.xz
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get_online_cpus() is a heavy weight function which involves a global
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mutex. migrate_disable() wants a simpler construct which prevents only
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a CPU from going doing while a task is in a migrate disabled section.
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Implement a per cpu lockless mechanism, which serializes only in the
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real unplug case on a global mutex. That serialization affects only
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tasks on the cpu which should be brought down.
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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include/linux/cpu.h | 5 +++++
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kernel/cpu.c | 15 +++++++++++++++
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kernel/sched/core.c | 4 ++++
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3 files changed, 24 insertions(+)
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--- a/include/linux/cpu.h
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+++ b/include/linux/cpu.h
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@@ -111,6 +111,8 @@ extern void cpu_hotplug_disable(void);
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extern void cpu_hotplug_enable(void);
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void clear_tasks_mm_cpumask(int cpu);
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int cpu_down(unsigned int cpu);
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+extern void pin_current_cpu(void);
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+extern void unpin_current_cpu(void);
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#else /* CONFIG_HOTPLUG_CPU */
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@@ -122,6 +124,9 @@ static inline int cpus_read_trylock(voi
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static inline void lockdep_assert_cpus_held(void) { }
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static inline void cpu_hotplug_disable(void) { }
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static inline void cpu_hotplug_enable(void) { }
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+static inline void pin_current_cpu(void) { }
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+static inline void unpin_current_cpu(void) { }
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+
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#endif /* !CONFIG_HOTPLUG_CPU */
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/* Wrappers which go away once all code is converted */
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--- a/kernel/cpu.c
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+++ b/kernel/cpu.c
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@@ -280,6 +280,21 @@ static int cpu_hotplug_disabled;
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#ifdef CONFIG_HOTPLUG_CPU
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+/**
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+ * pin_current_cpu - Prevent the current cpu from being unplugged
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+ */
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+void pin_current_cpu(void)
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+{
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+
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+}
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+
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+/**
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+ * unpin_current_cpu - Allow unplug of current cpu
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+ */
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+void unpin_current_cpu(void)
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+{
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+}
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+
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DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);
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void cpus_read_lock(void)
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--- a/kernel/sched/core.c
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+++ b/kernel/sched/core.c
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@@ -7197,6 +7197,7 @@ void migrate_disable(void)
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}
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preempt_disable();
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+ pin_current_cpu();
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migrate_disable_update_cpus_allowed(p);
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p->migrate_disable = 1;
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@@ -7262,12 +7263,15 @@ void migrate_enable(void)
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arg.task = p;
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arg.dest_cpu = dest_cpu;
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+ unpin_current_cpu();
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preempt_enable();
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stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
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tlb_migrate_finish(p->mm);
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+
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return;
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}
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}
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+ unpin_current_cpu();
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preempt_enable();
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}
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EXPORT_SYMBOL(migrate_enable);
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