On Mon, Jul 01, 2019 at 11:59:50PM -0700, Ian Rogers wrote:
> +#ifndef CONFIG_CGROUP_PERF
> + /*
> + * Without cgroups, with a task context, iterate over per-CPU and any
> + * CPU events.
> + */
> + const int max_itrs = 2;
> +#else
> + /*
> + * The depth of cgroups is limited by MAX_PATH. It is unlikely that this
> + * many parent-child related cgroups will have perf events
> + * monitored. Limit the number of cgroup iterators to 16.
> + */
> + const int max_cgroups_with_events_depth = 16;
> + /*
> + * With cgroups we either iterate for a task context (per-CPU or any CPU
> + * events) or for per CPU the global and per cgroup events.
> + */
> + const int max_itrs = max(2, 1 + max_cgroups_with_events_depth);
That seems like a very complicated way to write 17.
> +#endif
> + /* The number of iterators in use. */
> + int num_itrs;
> + /*
> + * A set of iterators, the iterator for the visit is chosen by the
> + * group_index.
> + */
> + struct perf_event *itrs[max_itrs];
And that is 136 bytes of stack. Which I suppose is just about
acceptible.
But why not something like:
struct perf_event *iters[IS_ENABLED(CONFIG_CGROUP_PERF) ? 17 : 2];
iters[i++] = foo;
WARN_ON_ONCE(i >= ARRAY_SIZE(iters));
?
