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

Alexey Budankov
2017-05-29T16:41:17Z

On 29.05.2017 18:29, Peter Zijlstra wrote:
> On Mon, May 29, 2017 at 05:22:54PM +0200, Peter Zijlstra wrote:
>> On Mon, May 29, 2017 at 04:43:09PM +0300, Alexey Budankov wrote:
>>> On 29.05.2017 15:03, Alexander Shishkin wrote:
>>>> Alexey Budankov <alexey.budankov@linux.intel.com> writes:
>>
>>>>> + } else if (event->cpu > node_event->cpu) {
>>>>> + node = &((*node)->rb_right);
>>>>> + } else {
>>>>> + list_add_tail(&event->group_list_entry,
>>>>> + &node_event->group_list);
>>>>
>>>> So why is this better than simply having per-cpu event lists plus one
>>>> for per-thread events?
>>>
>>> Good question. Choice of data structure and layout depends on the operations
>>> applied to the data so keeping groups as a tree simplifies and improves the
>>> implementation in terms of scalability and performance. Please ask more if
>>> any.
>>
>> Since these lists are per context, and each task can have a context,
>> you'd end up with per-task-per-cpu memory, which is something we'd like
>> to avoid (some archs have very limited per-cpu memory space etc..).

Aw, yeah. Memory consumption does matter in the kernel space.

>>
>> Also, we'd like to have that tree for other reasons, like for instance
>> that heterogeneous PMU crud ARM has. Also, with a tree we can easier do
>> time based round-robin scheduling,
>>
>
> Oh and in general multi-PMU stuff, aside from hetero PMU becomes much
> easier.
>