Re: [RFC] lib: optimize cpumask_local_spread()

[Michal Hocko]

On Thu 17-10-19 18:23:08, Shaokun Zhang wrote:
> From: yuqi jin <jinyuqi@xxxxxxxxxx>
> 
> In the multi-processor and NUMA system, A device may have many numa
> nodes belonging to multiple cpus. When we get a local numa, it is better
> to find the node closest to the local numa node to return instead of
> going to the online cpu immediately.
> 
> For example, In Huawei Kunpeng 920 system, there are 4 NUMA node(0 -3)
> in the 2-socket system(0 - 1). If the I/O device is in socket1
> and the local NUMA node is 2, we shall choose the non-local node3 in
> the same socket when cpu core in NUMA node2 is less that I/O requirements.
> If we directly pick one cpu core from all online ones, it may be in
> the another socket and it is not friendly for performance.

Could you be more specific on the effect of this patch please? Do you
have any performance numbers?
Also is it safe and reasonable to perform GFP_KERNEL (aka sleepable)
allocations from this function?

> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> Cc: Paul Burton <paul.burton@xxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Signed-off-by: yuqi jin <jinyuqi@xxxxxxxxxx>
> Signed-off-by: Shaokun Zhang <zhangshaokun@xxxxxxxxxxxxx>
> ---
>  lib/cpumask.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 67 insertions(+), 11 deletions(-)
> 
> diff --git a/lib/cpumask.c b/lib/cpumask.c
> index 0cb672eb107c..8f89c7cebfb0 100644
> --- a/lib/cpumask.c
> +++ b/lib/cpumask.c
> @@ -192,6 +192,33 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask)
>  }
>  #endif
>  
> +static void calc_node_distance(int *node_dist, int node)
> +{
> +	int i;
> +
> +	for (i = 0; i < nr_node_ids; i++)
> +		node_dist[i] = node_distance(node, i);
> +}
> +
> +static int find_nearest_node(int *node_dist, bool *used_flag)
> +{
> +	int i, min_dist = node_dist[0], node_id = -1;
> +
> +	for (i = 0; i < nr_node_ids; i++)
> +		if (used_flag[i] == 0) {
> +			min_dist = node_dist[i];
> +			node_id = i;
> +			break;
> +		}
> +	for (i = 0; i < nr_node_ids; i++)
> +		if (node_dist[i] < min_dist && used_flag[i] == 0) {
> +			min_dist = node_dist[i];
> +			node_id = i;
> +		}
> +
> +	return node_id;
> +}
> +
>  /**
>   * cpumask_local_spread - select the i'th cpu with local numa cpu's first
>   * @i: index number
> @@ -205,7 +232,8 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask)
>   */
>  unsigned int cpumask_local_spread(unsigned int i, int node)
>  {
> -	int cpu;
> +	int cpu, j, id, *node_dist;
> +	bool *used_flag;
>  
>  	/* Wrap: we always want a cpu. */
>  	i %= num_online_cpus();
> @@ -215,19 +243,47 @@ unsigned int cpumask_local_spread(unsigned int i, int node)
>  			if (i-- == 0)
>  				return cpu;
>  	} else {
> -		/* NUMA first. */
> -		for_each_cpu_and(cpu, cpumask_of_node(node), cpu_online_mask)
> -			if (i-- == 0)
> -				return cpu;
> +		node_dist = kmalloc_array(nr_node_ids,
> +			sizeof(int), GFP_KERNEL);
> +		if (!node_dist)
> +			for_each_cpu(cpu, cpu_online_mask)
> +				if (i-- == 0)
> +					return cpu;
>  
> -		for_each_cpu(cpu, cpu_online_mask) {
> -			/* Skip NUMA nodes, done above. */
> -			if (cpumask_test_cpu(cpu, cpumask_of_node(node)))
> -				continue;
> +		used_flag = kmalloc_array(nr_node_ids,
> +			sizeof(bool), GFP_KERNEL);
> +		if (!used_flag)
> +			for_each_cpu(cpu, cpu_online_mask)
> +				if (i-- == 0) {
> +					kfree(node_dist);
> +					return cpu;
> +				}
> +		memset(used_flag, 0, nr_node_ids * sizeof(bool));
>  
> -			if (i-- == 0)
> -				return cpu;
> +		calc_node_distance(node_dist, node);
> +		for (j = 0; j < nr_node_ids; j++) {
> +			id = find_nearest_node(node_dist, used_flag);
> +			if (id < 0)
> +				break;
> +			for_each_cpu_and(cpu,
> +				cpumask_of_node(id), cpu_online_mask)
> +				if (i-- == 0) {
> +					kfree(node_dist);
> +					kfree(used_flag);
> +					return cpu;
> +				}
> +			used_flag[id] = 1;
>  		}
> +
> +		for_each_cpu(cpu, cpu_online_mask)
> +			if (i-- == 0) {
> +				kfree(node_dist);
> +				kfree(used_flag);
> +				return cpu;
> +			}
> +
> +		kfree(node_dist);
> +		kfree(used_flag);
>  	}
>  	BUG();
>  }
> -- 
> 2.7.4

-- 
Michal Hocko
SUSE Labs