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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Date:   Mon, 29 May 2017 12:15:14 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 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