Messages in this thread | | | Date | Mon, 29 May 2017 17:22:54 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH]: perf/core: addressing 4x slowdown during per-process profiling of STREAM benchmark on Intel Xeon Phi |
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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..).
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,
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