Messages in this thread | | | Date | Wed, 7 Nov 2018 14:35:04 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v5 03/15] sched/core: uclamp: map TASK's clamp values into CPU's clamp groups |
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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; > +}
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