On Mon, Oct 29, 2018 at 06:32:57PM +0000, Patrick Bellasi wrote:
> +/**
> + * uclamp_group_get: increase the reference count for a clamp group
> + * @uc_se: the utilization clamp data for the task
> + * @clamp_id: the clamp index affected by the task
> + * @clamp_value: the new clamp value for the task
> + *
> + * Each time a task changes its utilization clamp value, for a specified
> clamp
> + * index, we need to find an available clamp group which can be used to track
> + * this new clamp value. The corresponding clamp group index will be used to
> + * reference count the corresponding clamp value while the task is enqueued
> on
> + * a CPU.
> + */
> +static void uclamp_group_get(struct uclamp_se *uc_se, unsigned int clamp_id,
> + unsigned int clamp_value)
> +{
> + union uclamp_map *uc_maps = &uclamp_maps[clamp_id][0];
> + unsigned int prev_group_id = uc_se->group_id;
> + union uclamp_map uc_map_old, uc_map_new;
> + unsigned int free_group_id;
> + unsigned int group_id;
> + unsigned long res;
> +
> +retry:
> +
> + free_group_id = UCLAMP_GROUPS;
> + for (group_id = 0; group_id < UCLAMP_GROUPS; ++group_id) {
> + uc_map_old.data = atomic_long_read(&uc_maps[group_id].adata);
> + if (free_group_id == UCLAMP_GROUPS && !uc_map_old.se_count)
> + free_group_id = group_id;
> + if (uc_map_old.value == clamp_value)
> + break;
> + }
> + if (group_id >= UCLAMP_GROUPS) {
> +#ifdef CONFIG_SCHED_DEBUG
> +#define UCLAMP_MAPERR "clamp value [%u] mapping to clamp group failed\n"
> + if (unlikely(free_group_id == UCLAMP_GROUPS)) {
> + pr_err_ratelimited(UCLAMP_MAPERR, clamp_value);
> + return;
> + }
> +#endif
> + group_id = free_group_id;
> + uc_map_old.data = atomic_long_read(&uc_maps[group_id].adata);
> + }
You forgot to check for refcount overflow here ;-)
And I'm not really a fan of hiding that error in a define like you keep
doing.
What's wrong with something like:
if (SCHED_WARN(free_group_id == UCLAMP_GROUPS))
return;
and
> + uc_map_new.se_count = uc_map_old.se_count + 1;
if (SCHED_WARN(!new.se_count))
new.se_count = -1;
> + uc_map_new.value = clamp_value;
> + res = atomic_long_cmpxchg(&uc_maps[group_id].adata,
> + uc_map_old.data, uc_map_new.data);
> + if (res != uc_map_old.data)
> + goto retry;
> +
> + /* Update SE's clamp values and attach it to new clamp group */
> + uc_se->value = clamp_value;
> + uc_se->group_id = group_id;
> +
> + /* Release the previous clamp group */
> + if (uc_se->mapped)
> + uclamp_group_put(clamp_id, prev_group_id);
> + uc_se->mapped = true;
> +}
