Re: [PATCH 1/3] perf bench numa: fix incorrect NUMA toplogy assumption

[Alexander Gordeev]

On Mon, Jun 29, 2020 at 05:50:07PM +0200, Alexander Gordeev wrote:
> The current code assumes that CPUs are evenly spread among
> NUMA nodes. That is generally incorrect and leads to failure
> on systems that have different NUMA topology.
> 
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Signed-off-by: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
> ---
>  tools/perf/bench/numa.c | 27 +++++++++++++--------------
>  1 file changed, 13 insertions(+), 14 deletions(-)
> 
> diff --git a/tools/perf/bench/numa.c b/tools/perf/bench/numa.c
> index 5797253..5497c74 100644
> --- a/tools/perf/bench/numa.c
> +++ b/tools/perf/bench/numa.c
> @@ -247,12 +247,13 @@ static int is_node_present(int node)
>   */
>  static bool node_has_cpus(int node)
>  {
> -	struct bitmask *cpu = numa_allocate_cpumask();
> +	struct bitmask *cpumask = numa_allocate_cpumask();
>  	unsigned int i;
>  
> -	if (cpu && !numa_node_to_cpus(node, cpu)) {
> -		for (i = 0; i < cpu->size; i++) {
> -			if (numa_bitmask_isbitset(cpu, i))
> +	BUG_ON(cpumask);

self-nack - should have been !cpumask,
will send the fixed version

> +	if (!numa_node_to_cpus(node, cpumask)) {
> +		for (i = 0; i < cpumask->size; i++) {
> +			if (numa_bitmask_isbitset(cpumask, i))
>  				return true;
>  		}
>  	}
> @@ -288,14 +289,10 @@ static cpu_set_t bind_to_cpu(int target_cpu)
>  
>  static cpu_set_t bind_to_node(int target_node)
>  {
> -	int cpus_per_node = g->p.nr_cpus / nr_numa_nodes();
>  	cpu_set_t orig_mask, mask;
>  	int cpu;
>  	int ret;
>  
> -	BUG_ON(cpus_per_node * nr_numa_nodes() != g->p.nr_cpus);
> -	BUG_ON(!cpus_per_node);
> -
>  	ret = sched_getaffinity(0, sizeof(orig_mask), &orig_mask);
>  	BUG_ON(ret);
>  
> @@ -305,13 +302,15 @@ static cpu_set_t bind_to_node(int target_node)
>  		for (cpu = 0; cpu < g->p.nr_cpus; cpu++)
>  			CPU_SET(cpu, &mask);
>  	} else {
> -		int cpu_start = (target_node + 0) * cpus_per_node;
> -		int cpu_stop  = (target_node + 1) * cpus_per_node;
> -
> -		BUG_ON(cpu_stop > g->p.nr_cpus);
> +		struct bitmask *cpumask = numa_allocate_cpumask();
>  
> -		for (cpu = cpu_start; cpu < cpu_stop; cpu++)
> -			CPU_SET(cpu, &mask);
> +		BUG_ON(!cpumask);
> +		if (!numa_node_to_cpus(target_node, cpumask)) {
> +			for (cpu = 0; cpu < (int)cpumask->size; cpu++) {
> +				if (numa_bitmask_isbitset(cpumask, cpu))
> +					CPU_SET(cpu, &mask);
> +			}
> +		}
>  	}
>  
>  	ret = sched_setaffinity(0, sizeof(mask), &mask);
> -- 
> 1.8.3.1
>