Re: [PATCH]: perf/core: addressing 4x slowdown during per-process profiling of STREAM benchmark on Intel Xeon Phi

[Alexander Shishkin]

Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx> writes:

Here (above the function) you could include a comment describing what
happens when this is called, locking considerations, etc.

> +static int
> +perf_cpu_tree_insert(struct rb_root *tree, struct perf_event *event)
> +{
> +	struct rb_node **node;
> +	struct rb_node *parent;
> +
> +	if (!tree || !event)
> +		return 0;

I don't think this should be happening, should it? And either way you
probably don't want to return 0 here, unless you're using !0 for
success.

> +
> +	node = &tree->rb_node;
> +	parent = *node;
> +
> +	while (*node) {
> +		struct perf_event *node_event =	container_of(*node,
> +				struct perf_event, group_node);
> +
> +		parent = *node;
> +
> +		if (event->cpu < node_event->cpu) {
> +			node = &((*node)->rb_left);

this would be the same as node = &parent->rb_left, right?

> +		} else if (event->cpu > node_event->cpu) {
> +			node = &((*node)->rb_right);
> +		} else {
> +			list_add_tail(&event->group_list_entry,
> +					&node_event->group_list);

So why is this better than simply having per-cpu event lists plus one
for per-thread events?

Also,

> +			return 2;

2?

> +		}
> +	}
> +
> +	list_add_tail(&event->group_list_entry, &event->group_list);
> +
> +	rb_link_node(&event->group_node, parent, node);
> +	rb_insert_color(&event->group_node, tree);
> +
> +	return 1;

Oh, you are using !0 for success. I guess it's a good thing you're not
actually checking its return code at the call site.

Regards,
--
Alex