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Commit16b269436b("sched/deadline: Modify cpudl::free_cpus to reflect rd->online") introduced the cpudl_set/clear_freecpu functions to allow the cpu_dl::free_cpus mask to be manipulated by the deadline scheduler class rq_on/offline callbacks so the mask would also reflect this state. Commit9659e1eeee("sched/deadline: Remove cpu_active_mask from cpudl_find()") removed the check of the cpu_active_mask to save some processing on the premise that the cpudl::free_cpus mask already reflected the runqueue online state. Unfortunately, there are cases where it is possible for the cpudl_clear function to set the free_cpus bit for a CPU when the deadline runqueue is offline. When this occurs while a CPU is connected to the default root domain the flag may retain the bad state after the CPU has been unplugged. Later, a different CPU that is transitioning through the default root domain may push a deadline task to the powered down CPU when cpudl_find sees its free_cpus bit is set. If this happens the task will not have the opportunity to run. One example is outlined here: https://lore.kernel.org/lkml/20250110233010.2339521-1-opendmb@gmail.com Another occurs when the last deadline task is migrated from a CPU that has an offlined runqueue. The dequeue_task member of the deadline scheduler class will eventually call cpudl_clear and set the free_cpus bit for the CPU. This commit modifies the cpudl_clear function to be aware of the online state of the deadline runqueue so that the free_cpus mask can be updated appropriately. It is no longer necessary to manage the mask outside of the cpudl_set/clear functions so the cpudl_set/clear_freecpu functions are removed. In addition, since the free_cpus mask is now only updated under the cpudl lock the code was changed to use the non-atomic __cpumask functions. Signed-off-by: Doug Berger <opendmb@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
24 lines
557 B
C
24 lines
557 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#include <linux/types.h>
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#include <linux/spinlock.h>
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#define IDX_INVALID -1
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struct cpudl_item {
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u64 dl;
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int cpu;
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int idx;
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};
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struct cpudl {
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raw_spinlock_t lock;
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int size;
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cpumask_var_t free_cpus;
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struct cpudl_item *elements;
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};
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int cpudl_find(struct cpudl *cp, struct task_struct *p, struct cpumask *later_mask);
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void cpudl_set(struct cpudl *cp, int cpu, u64 dl);
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void cpudl_clear(struct cpudl *cp, int cpu, bool online);
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int cpudl_init(struct cpudl *cp);
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void cpudl_cleanup(struct cpudl *cp);
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