Re: [PATCH 3/8] sched: Select a preferred node with the most numahinting faults

[Srikar Dronamraju]

* Mel Gorman <mgorman@xxxxxxx> [2013-06-26 15:38:02]:

> This patch selects a preferred node for a task to run on based on the
> NUMA hinting faults. This information is later used to migrate tasks
> towards the node during balancing.
> 
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> ---
>  include/linux/sched.h |  1 +
>  kernel/sched/core.c   | 10 ++++++++++
>  kernel/sched/fair.c   | 16 ++++++++++++++--
>  kernel/sched/sched.h  |  2 +-
>  4 files changed, 26 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 72861b4..ba46a64 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1507,6 +1507,7 @@ struct task_struct {
>  	struct callback_head numa_work;
>  
>  	unsigned long *numa_faults;
> +	int numa_preferred_nid;
>  #endif /* CONFIG_NUMA_BALANCING */
>  
>  	struct rcu_head rcu;
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index f332ec0..019baae 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1593,6 +1593,7 @@ static void __sched_fork(struct task_struct *p)
>  	p->numa_scan_seq = p->mm ? p->mm->numa_scan_seq : 0;
>  	p->numa_migrate_seq = p->mm ? p->mm->numa_scan_seq - 1 : 0;
>  	p->numa_scan_period = sysctl_numa_balancing_scan_delay;
> +	p->numa_preferred_nid = -1;

Though we may not want to inherit faults, I think the tasks generally
share pages with their siblings, parent. So will it make sense to
inherit the preferred node?

>  	p->numa_work.next = &p->numa_work;
>  	p->numa_faults = NULL;
>  #endif /* CONFIG_NUMA_BALANCING */
> @@ -5713,6 +5714,15 @@ enum s_alloc {
>  
>  struct sched_domain_topology_level;
>  
> +#ifdef CONFIG_NUMA_BALANCING
> +
> +/* Set a tasks preferred NUMA node */
> +void sched_setnuma(struct task_struct *p, int nid)
> +{
> +	p->numa_preferred_nid = nid;
> +}
> +#endif /* CONFIG_NUMA_BALANCING */
> +
>  typedef struct sched_domain *(*sched_domain_init_f)(struct sched_domain_topology_level *tl, int cpu);
>  typedef const struct cpumask *(*sched_domain_mask_f)(int cpu);
>  
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 904fd6f..f8c3f61 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -793,7 +793,8 @@ unsigned int sysctl_numa_balancing_scan_delay = 1000;
>  
>  static void task_numa_placement(struct task_struct *p)
>  {
> -	int seq;
> +	int seq, nid, max_nid = 0;
> +	unsigned long max_faults = 0;
>  
>  	if (!p->mm)	/* for example, ksmd faulting in a user's mm */
>  		return;
> @@ -802,7 +803,18 @@ static void task_numa_placement(struct task_struct *p)
>  		return;
>  	p->numa_scan_seq = seq;
>  
> -	/* FIXME: Scheduling placement policy hints go here */
> +	/* Find the node with the highest number of faults */
> +	for (nid = 0; nid < nr_node_ids; nid++) {
> +		unsigned long faults = p->numa_faults[nid];
> +		p->numa_faults[nid] >>= 1;
> +		if (faults > max_faults) {
> +			max_faults = faults;
> +			max_nid = nid;
> +		}
> +	}
> +
> +	if (max_faults && max_nid != p->numa_preferred_nid)
> +		sched_setnuma(p, max_nid);
>  }
>  
>  /*
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 9c26d88..65a0cf0 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -504,7 +504,7 @@ DECLARE_PER_CPU(struct rq, runqueues);
>  #define raw_rq()		(&__raw_get_cpu_var(runqueues))
>  
>  #ifdef CONFIG_NUMA_BALANCING
> -extern void sched_setnuma(struct task_struct *p, int node, int shared);
> +extern void sched_setnuma(struct task_struct *p, int nid);
>  static inline void task_numa_free(struct task_struct *p)
>  {
>  	kfree(p->numa_faults);
> -- 
> 1.8.1.4
> 
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-- 
Thanks and Regards
Srikar Dronamraju

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