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

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Message-ID: <20170620163728.GC26710@leverpostej>
Date:   Tue, 20 Jun 2017 17:37:28 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        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>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/n] perf/core: addressing 4x slowdown during
 per-process profiling of STREAM benchmark on Intel Xeon Phi

On Tue, Jun 20, 2017 at 06:22:56PM +0300, Alexey Budankov wrote:
> 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?

Yes; *every* group leader would be directly in the threaded rb tree.

> Which objects does the head keep?

Sorry, I'm not sure how to answer that. Did the above clarify?

If not, could you rephrase the question?

Thanks,
Mark.