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Subject: Re: [PATCH v2]: perf/core: addressing 4x slowdown during per-process,
 profiling of STREAM benchmark on Intel Xeon Phi
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Andi Kleen <ak@linux.intel.com>, Kan Liang <kan.liang@intel.com>,
        Dmitri Prokhorov <Dmitry.Prohorov@intel.com>,
        Valery Cherepennikov <valery.cherepennikov@intel.com>,
        David Carrillo-Cisneros <davidcc@google.com>,
        Stephane Eranian <eranian@google.com>,
        Mark Rutland <mark.rutland@arm.com>, linux-kernel@vger.kernel.org
References: <1e962b59-3e39-e0d6-515d-c4fd3502edae@linux.intel.com>
 <b410f376-69ed-c681-8413-c4186bc74aed@linux.intel.com>
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 <20170529104304.vy47zhf6fdq6bki3@hirez.programming.kicks-ass.net>
From: Alexey Budankov <alexey.budankov@linux.intel.com>
Organization: Intel Corp.
Message-ID: <0e8d266e-ea38-baea-765d-cab98df9b9bc@linux.intel.com>
Date: Mon, 29 May 2017 13:56:05 +0300
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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