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 13:43, Peter Zijlstra wrote:
> On Mon, May 29, 2017 at 12:15:14PM +0300, Alexey Budankov wrote:
> > On 29.05.2017 10:46, Peter Zijlstra wrote:
> > > On Sat, May 27, 2017 at 02:19:51PM +0300, Alexey Budankov wrote:
>
> > > > @@ -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.
>
> *confused*, what?
>
> Why can't the tree do both?

Well, indeed, the tree provides such capability too. However switching 
to the full tree iteration in cases where we now go through _groups 
lists will enlarge the patch, what is probably is not a big deal. Do you 
think it is worth implementing the switch?

Thanks,
Alexey