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

Peter Zijlstra
2017-05-29T10:43:14Z

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?