Messages in this thread | | | Subject | Re: [PATCH v3 1/n] perf/core: addressing 4x slowdown during per-process profiling of STREAM benchmark on Intel Xeon Phi | From | Alexey Budankov <> | Date | Fri, 16 Jun 2017 17:08:27 +0300 |
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On 16.06.2017 12:09, Mark Rutland wrote: > On Fri, Jun 16, 2017 at 01:10:10AM +0300, Alexey Budankov wrote: >> On 15.06.2017 22:56, Mark Rutland wrote: >>> On Thu, Jun 15, 2017 at 08:41:42PM +0300, Alexey Budankov wrote: >>>> This series of patches continues v2 and addresses captured comments. > >>>> Specifically this patch replaces pinned_groups and flexible_groups >>>> lists of perf_event_context by red-black cpu indexed trees avoiding >>>> data structures duplication and introducing possibility to iterate >>>> event groups for a specific CPU only. >>> >>> If you use --per-thread, I take it the overhead is significantly >>> lowered? >> >> Please ask more. > > IIUC, you're seeing the slowdown when using perf record, correct?
Correct. Specifically in per-process mode - without -a option.
> > There's a --per-thread option to ask perf record to not duplicate the > event per-cpu. > > If you use that, what amount of slowdown do you see? > > It might be preferable to not open task-bound per-cpu events on systems > with large cpu counts, and it would be good to know what the trade-off > looks like for this case. > >>>> +static void >>>> +perf_cpu_tree_insert(struct rb_root *tree, struct perf_event *event) >>>> +{ >>>> + struct rb_node **node; >>>> + struct rb_node *parent; >>>> + >>>> + WARN_ON_ONCE(!tree || !event); >>>> + >>>> + node = &tree->rb_node; >>>> + parent = *node; >>> >>> The first iteration of the loop handles this, so it can go. >> >> If tree is empty parent will be uninitialized what is harmful. > > Sorry; my bad. > > Thanks, > Mark. >
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