89 lines
2.8 KiB
Diff
89 lines
2.8 KiB
Diff
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Fri, 6 Jul 2018 15:06:15 +0200
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Subject: [PATCH] sched/core: Remove get_cpu() from sched_fork()
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.18/older/patches-4.18.7-rt5.tar.xz
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[ Upstream commit af0fffd9300b97d8875aa745bc78e2f6fdb3c1f0 ]
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get_cpu() disables preemption for the entire sched_fork() function.
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This get_cpu() was introduced in commit:
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dd41f596cda0 ("sched: cfs core code")
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... which also invoked sched_balance_self() and this function
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required preemption do be off.
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Today, sched_balance_self() seems to be moved to ->task_fork callback
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which is invoked while the ->pi_lock is held.
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set_load_weight() could invoke reweight_task() which then via $callchain
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might end up in smp_processor_id() but since `update_load' is false
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this won't happen.
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I didn't find any this_cpu*() or similar usage during the initialisation
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of the task_struct.
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The `cpu' value (from get_cpu()) is only used later in __set_task_cpu()
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while the ->pi_lock lock is held.
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Based on this it is possible to remove get_cpu() and use
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smp_processor_id() for the `cpu' variable without breaking anything.
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Cc: Thomas Gleixner <tglx@linutronix.de>
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Link: http://lkml.kernel.org/r/20180706130615.g2ex2kmfu5kcvlq6@linutronix.de
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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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---
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kernel/sched/core.c | 13 ++++---------
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1 file changed, 4 insertions(+), 9 deletions(-)
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--- a/kernel/sched/core.c
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+++ b/kernel/sched/core.c
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@@ -2317,7 +2317,6 @@ static inline void init_schedstats(void)
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int sched_fork(unsigned long clone_flags, struct task_struct *p)
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{
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unsigned long flags;
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- int cpu = get_cpu();
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__sched_fork(clone_flags, p);
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/*
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@@ -2353,14 +2352,12 @@ int sched_fork(unsigned long clone_flags
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p->sched_reset_on_fork = 0;
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}
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- if (dl_prio(p->prio)) {
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- put_cpu();
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+ if (dl_prio(p->prio))
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return -EAGAIN;
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- } else if (rt_prio(p->prio)) {
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+ else if (rt_prio(p->prio))
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p->sched_class = &rt_sched_class;
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- } else {
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+ else
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p->sched_class = &fair_sched_class;
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- }
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init_entity_runnable_average(&p->se);
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@@ -2376,7 +2373,7 @@ int sched_fork(unsigned long clone_flags
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* We're setting the CPU for the first time, we don't migrate,
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* so use __set_task_cpu().
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*/
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- __set_task_cpu(p, cpu);
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+ __set_task_cpu(p, smp_processor_id());
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if (p->sched_class->task_fork)
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p->sched_class->task_fork(p);
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raw_spin_unlock_irqrestore(&p->pi_lock, flags);
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@@ -2393,8 +2390,6 @@ int sched_fork(unsigned long clone_flags
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plist_node_init(&p->pushable_tasks, MAX_PRIO);
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RB_CLEAR_NODE(&p->pushable_dl_tasks);
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#endif
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-
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- put_cpu();
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return 0;
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}
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