From d05b43059dfa115037cd37bc276a8316391def28 Mon Sep 17 00:00:00 2001 From: Vincent Donnefort Date: Tue, 21 Jun 2022 10:04:08 +0100 Subject: sched/fair: Provide u64 read for 32-bits arch helper Introducing macro helpers u64_u32_{store,load}() to factorize lockless accesses to u64 variables for 32-bits architectures. Users are for now cfs_rq.min_vruntime and sched_avg.last_update_time. To accommodate the later where the copy lies outside of the structure (cfs_rq.last_udpate_time_copy instead of sched_avg.last_update_time_copy), use the _copy() version of those helpers. Those new helpers encapsulate smp_rmb() and smp_wmb() synchronization and therefore, have a small penalty for 32-bits machines in set_task_rq_fair() and init_cfs_rq(). Signed-off-by: Vincent Donnefort Signed-off-by: Vincent Donnefort Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Dietmar Eggemann Tested-by: Lukasz Luba Link: https://lkml.kernel.org/r/20220621090414.433602-2-vdonnefort@google.com --- kernel/sched/fair.c | 84 +++++++++------------------------------------------- kernel/sched/sched.h | 41 ++++++++++++++++++++++++- 2 files changed, 54 insertions(+), 71 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index f80ae86bb404..8dc0903abc82 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -612,11 +612,8 @@ static void update_min_vruntime(struct cfs_rq *cfs_rq) } /* ensure we never gain time by being placed backwards. */ - cfs_rq->min_vruntime = max_vruntime(cfs_rq->min_vruntime, vruntime); -#ifndef CONFIG_64BIT - smp_wmb(); - cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime; -#endif + u64_u32_store(cfs_rq->min_vruntime, + max_vruntime(cfs_rq->min_vruntime, vruntime)); } static inline bool __entity_less(struct rb_node *a, const struct rb_node *b) @@ -3348,6 +3345,11 @@ static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags) } #ifdef CONFIG_SMP +static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq) +{ + return u64_u32_load_copy(cfs_rq->avg.last_update_time, + cfs_rq->last_update_time_copy); +} #ifdef CONFIG_FAIR_GROUP_SCHED /* * Because list_add_leaf_cfs_rq always places a child cfs_rq on the list @@ -3458,27 +3460,9 @@ void set_task_rq_fair(struct sched_entity *se, if (!(se->avg.last_update_time && prev)) return; -#ifndef CONFIG_64BIT - { - u64 p_last_update_time_copy; - u64 n_last_update_time_copy; - - do { - p_last_update_time_copy = prev->load_last_update_time_copy; - n_last_update_time_copy = next->load_last_update_time_copy; - - smp_rmb(); - - p_last_update_time = prev->avg.last_update_time; - n_last_update_time = next->avg.last_update_time; + p_last_update_time = cfs_rq_last_update_time(prev); + n_last_update_time = cfs_rq_last_update_time(next); - } while (p_last_update_time != p_last_update_time_copy || - n_last_update_time != n_last_update_time_copy); - } -#else - p_last_update_time = prev->avg.last_update_time; - n_last_update_time = next->avg.last_update_time; -#endif __update_load_avg_blocked_se(p_last_update_time, se); se->avg.last_update_time = n_last_update_time; } @@ -3831,12 +3815,9 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) } decayed |= __update_load_avg_cfs_rq(now, cfs_rq); - -#ifndef CONFIG_64BIT - smp_wmb(); - cfs_rq->load_last_update_time_copy = sa->last_update_time; -#endif - + u64_u32_store_copy(sa->last_update_time, + cfs_rq->last_update_time_copy, + sa->last_update_time); return decayed; } @@ -3968,27 +3949,6 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s } } -#ifndef CONFIG_64BIT -static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq) -{ - u64 last_update_time_copy; - u64 last_update_time; - - do { - last_update_time_copy = cfs_rq->load_last_update_time_copy; - smp_rmb(); - last_update_time = cfs_rq->avg.last_update_time; - } while (last_update_time != last_update_time_copy); - - return last_update_time; -} -#else -static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq) -{ - return cfs_rq->avg.last_update_time; -} -#endif - /* * Synchronize entity load avg of dequeued entity without locking * the previous rq. @@ -6968,21 +6928,8 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) if (READ_ONCE(p->__state) == TASK_WAKING) { struct sched_entity *se = &p->se; struct cfs_rq *cfs_rq = cfs_rq_of(se); - u64 min_vruntime; - -#ifndef CONFIG_64BIT - u64 min_vruntime_copy; - - do { - min_vruntime_copy = cfs_rq->min_vruntime_copy; - smp_rmb(); - min_vruntime = cfs_rq->min_vruntime; - } while (min_vruntime != min_vruntime_copy); -#else - min_vruntime = cfs_rq->min_vruntime; -#endif - se->vruntime -= min_vruntime; + se->vruntime -= u64_u32_load(cfs_rq->min_vruntime); } if (p->on_rq == TASK_ON_RQ_MIGRATING) { @@ -11508,10 +11455,7 @@ static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first) void init_cfs_rq(struct cfs_rq *cfs_rq) { cfs_rq->tasks_timeline = RB_ROOT_CACHED; - cfs_rq->min_vruntime = (u64)(-(1LL << 20)); -#ifndef CONFIG_64BIT - cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime; -#endif + u64_u32_store(cfs_rq->min_vruntime, (u64)(-(1LL << 20))); #ifdef CONFIG_SMP raw_spin_lock_init(&cfs_rq->removed.lock); #endif diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 02c970501295..8a3c8a0db660 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -520,6 +520,45 @@ struct cfs_bandwidth { }; #endif /* CONFIG_CGROUP_SCHED */ +/* + * u64_u32_load/u64_u32_store + * + * Use a copy of a u64 value to protect against data race. This is only + * applicable for 32-bits architectures. + */ +#ifdef CONFIG_64BIT +# define u64_u32_load_copy(var, copy) var +# define u64_u32_store_copy(var, copy, val) (var = val) +#else +# define u64_u32_load_copy(var, copy) \ +({ \ + u64 __val, __val_copy; \ + do { \ + __val_copy = copy; \ + /* \ + * paired with u64_u32_store_copy(), ordering access \ + * to var and copy. \ + */ \ + smp_rmb(); \ + __val = var; \ + } while (__val != __val_copy); \ + __val; \ +}) +# define u64_u32_store_copy(var, copy, val) \ +do { \ + typeof(val) __val = (val); \ + var = __val; \ + /* \ + * paired with u64_u32_load_copy(), ordering access to var and \ + * copy. \ + */ \ + smp_wmb(); \ + copy = __val; \ +} while (0) +#endif +# define u64_u32_load(var) u64_u32_load_copy(var, var##_copy) +# define u64_u32_store(var, val) u64_u32_store_copy(var, var##_copy, val) + /* CFS-related fields in a runqueue */ struct cfs_rq { struct load_weight load; @@ -560,7 +599,7 @@ struct cfs_rq { */ struct sched_avg avg; #ifndef CONFIG_64BIT - u64 load_last_update_time_copy; + u64 last_update_time_copy; #endif struct { raw_spinlock_t lock ____cacheline_aligned; -- cgit v1.2.3-59-g8ed1b