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a85c2257a8
Patch series "memcg, cpuisol: do not interfere pcp cache charges draining with cpuisol workloads". Leonardo has reported [1] that pcp memcg charge draining can interfere with cpu isolated workloads. The said draining is done from a WQ context with a pcp worker scheduled on each CPU which holds any cached charges for a specific memcg hierarchy. Operation is not really a common operation [2]. It can be triggered from the userspace though so some care is definitely due. Leonardo has tried to address the issue by allowing remote charge draining [3]. This approach requires an additional locking to synchronize pcp caches sync from a remote cpu from local pcp consumers. Even though the proposed lock was per-cpu there is still potential for contention and less predictable behavior. This patchset addresses the issue from a different angle. Rather than dealing with a potential synchronization, cpus which are isolated are simply never scheduled to be drained. This means that a small amount of charges could be laying around and waiting for a later use or they are flushed when a different memcg is charged from the same cpu. More details are in patch 2. The first patch from Frederic is implementing an abstraction to tell whether a specific cpu has been isolated and therefore require a special treatment. This patch (of 2): Provide this new API to check if a CPU has been isolated either through isolcpus= or nohz_full= kernel parameter. It aims at avoiding kernel load deemed to be safely spared on CPUs running sensitive workload that can't bear any disturbance, such as pcp cache draining. Link: https://lkml.kernel.org/r/20230317134448.11082-1-mhocko@kernel.org Link: https://lkml.kernel.org/r/20230317134448.11082-2-mhocko@kernel.org Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Michal Hocko <mhocko@suse.com> Suggested-by: Michal Hocko <mhocko@suse.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Muchun Song <muchun.song@linux.dev> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Shakeel Butt <shakeelb@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Leonardo Bras <leobras@redhat.com> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
73 lines
1.7 KiB
C
73 lines
1.7 KiB
C
#ifndef _LINUX_SCHED_ISOLATION_H
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#define _LINUX_SCHED_ISOLATION_H
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#include <linux/cpumask.h>
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#include <linux/init.h>
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#include <linux/tick.h>
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enum hk_type {
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HK_TYPE_TIMER,
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HK_TYPE_RCU,
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HK_TYPE_MISC,
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HK_TYPE_SCHED,
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HK_TYPE_TICK,
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HK_TYPE_DOMAIN,
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HK_TYPE_WQ,
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HK_TYPE_MANAGED_IRQ,
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HK_TYPE_KTHREAD,
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HK_TYPE_MAX
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};
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#ifdef CONFIG_CPU_ISOLATION
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DECLARE_STATIC_KEY_FALSE(housekeeping_overridden);
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extern int housekeeping_any_cpu(enum hk_type type);
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extern const struct cpumask *housekeeping_cpumask(enum hk_type type);
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extern bool housekeeping_enabled(enum hk_type type);
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extern void housekeeping_affine(struct task_struct *t, enum hk_type type);
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extern bool housekeeping_test_cpu(int cpu, enum hk_type type);
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extern void __init housekeeping_init(void);
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#else
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static inline int housekeeping_any_cpu(enum hk_type type)
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{
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return smp_processor_id();
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}
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static inline const struct cpumask *housekeeping_cpumask(enum hk_type type)
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{
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return cpu_possible_mask;
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}
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static inline bool housekeeping_enabled(enum hk_type type)
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{
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return false;
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}
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static inline void housekeeping_affine(struct task_struct *t,
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enum hk_type type) { }
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static inline bool housekeeping_test_cpu(int cpu, enum hk_type type)
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{
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return true;
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}
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static inline void housekeeping_init(void) { }
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#endif /* CONFIG_CPU_ISOLATION */
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static inline bool housekeeping_cpu(int cpu, enum hk_type type)
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{
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#ifdef CONFIG_CPU_ISOLATION
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if (static_branch_unlikely(&housekeeping_overridden))
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return housekeeping_test_cpu(cpu, type);
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#endif
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return true;
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}
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static inline bool cpu_is_isolated(int cpu)
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{
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return !housekeeping_test_cpu(cpu, HK_TYPE_DOMAIN) ||
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!housekeeping_test_cpu(cpu, HK_TYPE_TICK);
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}
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#endif /* _LINUX_SCHED_ISOLATION_H */
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