Re: [PATCH v2]: perf/core: addressing 4x slowdown during per-process, profiling of STREAM benchmark on Intel Xeon Phi

[Alexey Budankov]

On 29.05.2017 10:46, Peter Zijlstra wrote:
> On Sat, May 27, 2017 at 02:19:51PM +0300, Alexey Budankov wrote:
> > @@ -571,6 +587,27 @@ struct perf_event {
> >   	 * either sufficies for read.
> >   	 */
> >   	struct list_head		group_entry;
> > +	/*
> > +	 * Node on the pinned or flexible tree located at the event context;
> > +	 * the node may be empty in case its event is not directly attached
> > +	 * to the tree but to group_list list of the event directly
> > +	 * attached to the tree;
> > +	 */
> > +	struct rb_node			group_node;
> > +	/*
> > +	 * List keeps groups allocated for the same cpu;
> > +	 * the list may be empty in case its event is not directly
> > +	 * attached to the tree but to group_list list of the event directly
> > +	 * attached to the tree;
> > +	 */
> > +	struct list_head		group_list;
> > +	/*
> > +	 * Entry into the group_list list above;
> > +	 * the entry may be attached to the self group_list list above
> > +	 * in case the event is directly attached to the pinned or
> > +	 * flexible tree;
> > +	 */
> > +	struct list_head		group_list_entry;
> >   	struct list_head		sibling_list;
> >
> >   	/*
>
> > @@ -742,7 +772,17 @@ struct perf_event_context {
> >
> >   	struct list_head		active_ctx_list;
> >   	struct list_head		pinned_groups;
> > +	/*
> > +	 * Cpu tree for pinned groups; keeps event's group_node nodes
> > +	 * of attached flexible groups;
> > +	 */
> > +	struct rb_root			pinned_tree;
> >   	struct list_head		flexible_groups;
> > +	/*
> > +	 * Cpu tree for flexible groups; keeps event's group_node nodes
> > +	 * of attached flexible groups;
> > +	 */
> > +	struct rb_root			flexible_tree;
> >   	struct list_head		event_list;
> >   	int				nr_events;
> >   	int				nr_active;
> > @@ -758,6 +798,7 @@ struct perf_event_context {
> >   	 */
> >   	u64				time;
> >   	u64				timestamp;
> > +	struct perf_event_tstamp	tstamp_data;
> >
> >   	/*
> >   	 * These fields let us detect when two contexts have both
>
>
> So why do we now have a list _and_ a tree for the same entries?
We need groups list to iterate through all groups configured for 
collection and we need the tree to quickly iterate through the groups 
allocated for a particular CPU only.
>

-Alexey