Re: [PATCH v2 3/3] tools/sched_ext: add arena based scheduler

[Tejun Heo <tj@kernel.org>]

Hello,

On Tue, Jan 13, 2026 at 11:48:18AM -0500, Emil Tsalapatis wrote:
...
> +__hidden
> +int scx_alloc_free_idx(struct scx_allocator *alloc, __u64 idx)
> +{
> +	const __u64 mask = (1 << SDT_TASK_ENTS_PER_PAGE_SHIFT) - 1;
> +	sdt_desc_t *lv_desc[SDT_TASK_LEVELS];
> +	sdt_desc_t * __arena *desc_children;
> +	struct sdt_chunk __arena *chunk;
> +	sdt_desc_t *desc;
> +	struct sdt_data __arena *data;
> +	__u64 level, shift, pos;
> +	__u64 lv_pos[SDT_TASK_LEVELS];
> +	int ret;
> +	int i;
> +
> +	if (!alloc)
> +		return 0;
> +
> +	desc = alloc->root;
> +	if (unlikely(!desc))
> +		return -EINVAL;
> +
> +	/* To appease the verifier. */
> +	for (level = zero; level < SDT_TASK_LEVELS && can_loop; level++) {
> +		lv_desc[level] = NULL;
> +		lv_pos[level] = 0;
> +	}
> +
> +	/* Find the leaf node containing the index. */
> +	for (level = zero; level < SDT_TASK_LEVELS && can_loop; level++) {
> +		shift = (SDT_TASK_LEVELS - 1 - level) * SDT_TASK_ENTS_PER_PAGE_SHIFT;
> +		pos = (idx >> shift) & mask;
> +
> +		lv_desc[level] = desc;
> +		lv_pos[level] = pos;
> +
> +		if (level == SDT_TASK_LEVELS - 1)
> +			break;
> +
> +		chunk = desc->chunk;
> +
> +		desc_children = (sdt_desc_t * __arena *)chunk->descs;
> +		desc = desc_children[pos];
> +
> +		if (unlikely(!desc))
> +			return -EINVAL;
> +	}
> +
> +	chunk = desc->chunk;
> +
> +	pos = idx & mask;
> +	data = chunk->data[pos];
> +	if (likely(!data)) {

AI review flagged this. Should this be "if (likely(data)) {"?

> +		data[pos] = (struct sdt_data) {
> +			.tid.genn = data->tid.genn + 1,
> +		};
> +
> +		/* Zero out one word at a time. */
> +		for (i = zero; i < alloc->pool.elem_size / 8 && can_loop; i++) {
> +			data->payload[i] = 0;
> +		}
> +	}

Thanks.

-- 
tejun