Re: [PATCH v3 1/n] perf/core: addressing 4x slowdown during per-process profiling of STREAM benchmark on Intel Xeon Phi

[Alexey Budankov]

On 20.06.2017 16:36, Mark Rutland wrote:
> On Mon, Jun 19, 2017 at 11:31:59PM +0300, Alexey Budankov wrote:
> > On 15.06.2017 22:56, Mark Rutland wrote:
> > > On Thu, Jun 15, 2017 at 08:41:42PM +0300, Alexey Budankov wrote:
> > > > +static int
> > > > +perf_cpu_tree_iterate(struct rb_root *tree,
> > > > +		perf_cpu_tree_callback_t callback, void *data)
> > > > +{
> > > > +	int ret = 0;
> > > > +	struct rb_node *node;
> > > > +	struct perf_event *event;
> > > > +
> > > > +	WARN_ON_ONCE(!tree);
> > > > +
> > > > +	for (node = rb_first(tree); node; node = rb_next(node)) {
> > > > +		struct perf_event *node_event = container_of(node,
> > > > +				struct perf_event, group_node);
> > > > +
> > > > +		list_for_each_entry(event, &node_event->group_list,
> > > > +				group_list_entry) {
> > > > +			ret = callback(event, data);
> > > > +			if (ret)
> > > > +				return ret;
> > > > +		}
> > > > +	}
> > > > +
> > > > +	return 0;
> > > >   }
> > >
> > > If you need to iterate over every event, you can use the list that
> > > threads the whole tree.
> >
> > Could you please explain more on that?
>
> In Peter's original suggestion, we'd use a threaded tree rather than a
> tree of lists.
>
> i.e. you'd have something like:
>
> struct threaded_rb_node {
> 	struct rb_node   node;
> 	struct list_head head;
> };

Is this for every group leader? Which objects does the head keep?

> ... with the tree and list covering all nodes, in the same order:
>
> Tree:
>
>       3
>      / \
>     /   \
>    1     5
>   / \   / \
> 0   2 4   6
>
> List:
>
> 0 - 1 - 2 - 3 - 4 - 5 - 6
>
> ... that way you can search using the tree, and iterate using the list,
> even when you wan to iterate over sub-lists.
>
> Thanks,
> Mark.