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

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Message-ID: <20170529104304.vy47zhf6fdq6bki3@hirez.programming.kicks-ass.net>
Date:   Mon, 29 May 2017 12:43:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...el.com>,
        Dmitri Prokhorov <Dmitry.Prohorov@...el.com>,
        Valery Cherepennikov <valery.cherepennikov@...el.com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2]: perf/core: addressing 4x slowdown during
 per-process, profiling of STREAM benchmark on Intel Xeon Phi

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?