Messages in this thread | | | Date | Tue, 20 Jun 2017 17:38:50 +0100 | From | Mark Rutland <> | Subject | Re: [RESEND PATCH v3 1/n] perf/core: addressing 4x slowdown during per-process profiling of STREAM benchmark on Intel Xeon Phi |
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On Tue, Jun 20, 2017 at 06:12:08PM +0300, Alexey Budankov wrote: > On 20.06.2017 16:44, Mark Rutland wrote: > >On Fri, Jun 16, 2017 at 02:03:58AM +0300, Alexey Budankov wrote: > >>perf/core: use rb trees for pinned/flexible groups > >> > >>By default, the userspace perf tool opens per-cpu task-bound events > >>when sampling, so for N logical events requested by the user, the tool > >>will open N * NR_CPUS events. > >> > >>In the kernel, we mux events with a hrtimer, periodically rotating the > >>flexible group list and trying to schedule each group in turn. We > >>skip groups whose cpu filter doesn't match. So when we get unlucky, > >>we can walk N * (NR_CPUS - 1) groups pointlessly for each hrtimer > >>invocation. > >> > >>This has been observed to result in significant overhead when running > >>the STREAM benchmark on 272 core Xeon Phi systems. > >> > >>One way to avoid this is to place our events into an rb tree sorted by > >>CPU filter, so that our hrtimer can skip to the current CPU's > >>list and ignore everything else. > >> > >>As a step towards that, this patch replaces event group lists with rb > >>trees. > >> > >>Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com> > >>--- > >> include/linux/perf_event.h | 18 ++- > >> kernel/events/core.c | 393 > >>+++++++++++++++++++++++++++++++++------------ > >> 2 files changed, 307 insertions(+), 104 deletions(-) > >> > >>Addressed Mark Rutland's comments from the previous patch version. > > > >... then this should be v4, no? > > > >Which comments? Could you pelase write a changelog in future? > > Changes are: > > 1. changed type of pinned_groups/flexible_groups to rb_tree; > 2. removed group_list_entry and reused group_entry for that purposes; > 3. added add_to_groups()/del_from_groups() helper functions;
Thanks; the new changelog is much appreciated.
Mark.
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