[PATCH v2] drm/amdkfd: Try to schedule bottom half on same core

[Philip Yang]

On 2022-08-11 15:04, Felix Kuehling wrote:
> On systems that support SMT (hyperthreading) schedule the bottom half of
> the KFD interrupt handler on the same core. This makes it possible to
> reserve a core for interrupt handling and have the bottom half run on
> that same core.
>
> On systems without SMT, pick another core in the same NUMA node, as
> before.
>
> Use for_each_cpu_wrap instead of open-coding it.
>
> Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>

nit-pick below, looks better to use new_cpu as iterator, either way this is

Reviewed-by: Philip Yang <Philip.Yang at amd.com>

> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_device.c | 20 ++++++++++++++++----
>   1 file changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_device.c b/drivers/gpu/drm/amd/amdkfd/kfd_device.c
> index f5853835f03a..4d1284714e7a 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_device.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_device.c
> @@ -24,6 +24,7 @@
>   #include <linux/bsearch.h>
>   #include <linux/pci.h>
>   #include <linux/slab.h>
> +#include <linux/topology.h>
>   #include "kfd_priv.h"
>   #include "kfd_device_queue_manager.h"
>   #include "kfd_pm4_headers_vi.h"
> @@ -801,13 +802,24 @@ static inline void kfd_queue_work(struct workqueue_struct *wq,
>   				  struct work_struct *work)
>   {
>   	int cpu, new_cpu;
> +	const struct cpumask *mask = NULL;
>   
>   	cpu = new_cpu = smp_processor_id();
> -	do {
> -		new_cpu = cpumask_next(new_cpu, cpu_online_mask) % nr_cpu_ids;
> -		if (cpu_to_node(new_cpu) == numa_node_id())
> +
> +#if defined(CONFIG_SCHED_SMT)
> +	/* CPU threads in the same core */
> +	mask = cpu_smt_mask(cpu);
> +#endif
> +	if (!mask || cpumask_weight(mask) <= 1)
> +		/* CPU threads in the same NUMA node */
> +		mask = cpu_cpu_mask(cpu);
> +	/* Pick the next online CPU thread in the same core or NUMA node */
> +	for_each_cpu_wrap(cpu, mask, cpu+1) {
> +		if (cpu != new_cpu && cpu_online(cpu)) {
> +			new_cpu = cpu;
>   			break;
> -	} while (cpu != new_cpu);
> +		}
> +	}
>   
>   	queue_work_on(new_cpu, wq, work);
>   }

	for_each_cpu_wrap(new_cpu, mask, cpu + 1) {
		if (cpu != new_cpu && cpu_online(new_cpu)) {
			cpu = new_cpu;
  			break;
		}
	}
	queue_work_on(cpu, wq, work);