Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759340AbbLBSmt (ORCPT ); Wed, 2 Dec 2015 13:42:49 -0500 Received: from g1t6220.austin.hp.com ([15.73.96.84]:52360 "EHLO g1t6220.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756725AbbLBSmH (ORCPT ); Wed, 2 Dec 2015 13:42:07 -0500 From: Waiman Long To: Ingo Molnar , Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Yuyang Du , Paul Turner , Ben Segall , Morten Rasmussen , Scott J Norton , Douglas Hatch , Waiman Long Subject: [PATCH v2 2/3] sched/fair: Move hot load_avg into its own cacheline Date: Wed, 2 Dec 2015 13:41:49 -0500 Message-Id: <1449081710-20185-3-git-send-email-Waiman.Long@hpe.com> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1449081710-20185-1-git-send-email-Waiman.Long@hpe.com> References: <1449081710-20185-1-git-send-email-Waiman.Long@hpe.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5180 Lines: 148 If a system with large number of sockets was driven to full utilization, it was found that the clock tick handling occupied a rather significant proportion of CPU time when fair group scheduling and autogroup were enabled. Running a java benchmark on a 16-socket IvyBridge-EX system, the perf profile looked like: 10.52% 0.00% java [kernel.vmlinux] [k] smp_apic_timer_interrupt 9.66% 0.05% java [kernel.vmlinux] [k] hrtimer_interrupt 8.65% 0.03% java [kernel.vmlinux] [k] tick_sched_timer 8.56% 0.00% java [kernel.vmlinux] [k] update_process_times 8.07% 0.03% java [kernel.vmlinux] [k] scheduler_tick 6.91% 1.78% java [kernel.vmlinux] [k] task_tick_fair 5.24% 5.04% java [kernel.vmlinux] [k] update_cfs_shares In particular, the high CPU time consumed by update_cfs_shares() was mostly due to contention on the cacheline that contained the task_group's load_avg statistical counter. This cacheline may also contains variables like shares, cfs_rq & se which are accessed rather frequently during clock tick processing. This patch moves the load_avg variable into another cacheline separated from the other frequently accessed variables. It also creates a cacheline aligned kmemcache for task_group to make sure that all the allocated task_group's are cacheline aligned. By doing so, the perf profile became: 9.44% 0.00% java [kernel.vmlinux] [k] smp_apic_timer_interrupt 8.74% 0.01% java [kernel.vmlinux] [k] hrtimer_interrupt 7.83% 0.03% java [kernel.vmlinux] [k] tick_sched_timer 7.74% 0.00% java [kernel.vmlinux] [k] update_process_times 7.27% 0.03% java [kernel.vmlinux] [k] scheduler_tick 5.94% 1.74% java [kernel.vmlinux] [k] task_tick_fair 4.15% 3.92% java [kernel.vmlinux] [k] update_cfs_shares The %cpu time is still pretty high, but it is better than before. The benchmark results before and after the patch was as follows: Before patch - Max-jOPs: 907533 Critical-jOps: 134877 After patch - Max-jOPs: 916011 Critical-jOps: 142366 Signed-off-by: Waiman Long --- kernel/sched/core.c | 36 ++++++++++++++++++++++++++++++++++-- kernel/sched/sched.h | 7 ++++++- 2 files changed, 40 insertions(+), 3 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 4d568ac..e39204f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7331,6 +7331,11 @@ int in_sched_functions(unsigned long addr) */ struct task_group root_task_group; LIST_HEAD(task_groups); + +#ifdef CONFIG_FAIR_GROUP_SCHED +/* Cacheline aligned slab cache for task_group */ +static struct kmem_cache *task_group_cache __read_mostly; +#endif #endif DECLARE_PER_CPU(cpumask_var_t, load_balance_mask); @@ -7356,6 +7361,7 @@ void __init sched_init(void) root_task_group.cfs_rq = (struct cfs_rq **)ptr; ptr += nr_cpu_ids * sizeof(void **); + task_group_cache = KMEM_CACHE(task_group, SLAB_HWCACHE_ALIGN); #endif /* CONFIG_FAIR_GROUP_SCHED */ #ifdef CONFIG_RT_GROUP_SCHED root_task_group.rt_se = (struct sched_rt_entity **)ptr; @@ -7668,12 +7674,38 @@ void set_curr_task(int cpu, struct task_struct *p) /* task_group_lock serializes the addition/removal of task groups */ static DEFINE_SPINLOCK(task_group_lock); +/* + * Make sure that the task_group structure is cacheline aligned when + * fair group scheduling is enabled. + */ +#ifdef CONFIG_FAIR_GROUP_SCHED +static inline struct task_group *alloc_task_group(void) +{ + return kmem_cache_alloc(task_group_cache, GFP_KERNEL | __GFP_ZERO); +} + +static inline void free_task_group(struct task_group *tg) +{ + kmem_cache_free(task_group_cache, tg); +} +#else /* CONFIG_FAIR_GROUP_SCHED */ +static inline struct task_group *alloc_task_group(void) +{ + return kzalloc(sizeof(struct task_group), GFP_KERNEL); +} + +static inline void free_task_group(struct task_group *tg) +{ + kfree(tg); +} +#endif /* CONFIG_FAIR_GROUP_SCHED */ + static void free_sched_group(struct task_group *tg) { free_fair_sched_group(tg); free_rt_sched_group(tg); autogroup_free(tg); - kfree(tg); + free_task_group(tg); } /* allocate runqueue etc for a new task group */ @@ -7681,7 +7713,7 @@ struct task_group *sched_create_group(struct task_group *parent) { struct task_group *tg; - tg = kzalloc(sizeof(*tg), GFP_KERNEL); + tg = alloc_task_group(); if (!tg) return ERR_PTR(-ENOMEM); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index efd3bfc..e679895 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -248,7 +248,12 @@ struct task_group { unsigned long shares; #ifdef CONFIG_SMP - atomic_long_t load_avg; + /* + * load_avg can be heavily contended at clock tick time, so put + * it in its own cacheline separated from the fields above which + * will also be accessed at each tick. + */ + atomic_long_t load_avg ____cacheline_aligned; #endif #endif -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/