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 | Mon, 19 Jun 2017 17:09:00 +0300 |
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On 19.06.2017 16:38, Mark Rutland wrote: > On Mon, Jun 19, 2017 at 01:46:39PM +0100, Mark Rutland wrote: >> On Fri, Jun 16, 2017 at 05:22:29PM +0300, Alexey Budankov wrote: >>> On 16.06.2017 17:08, Alexey Budankov wrote: >>>> On 16.06.2017 12:09, Mark Rutland wrote: >>>>> 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? >>> >>> After applying all three patches: >>> >>> - system-wide collection: >>> >>> [ perf record: Woken up 1 times to write data ] >>> [ perf record: Captured and wrote 303.795 MB perf.data (~13272985 samples) ] >>> 2162.08user 176.24system 0:12.97elapsed 18021%CPU (0avgtext+0avgdata >>> 1187208maxresident)k >>> 0inputs+622624outputs (0major+1360285minor)pagefaults 0swaps >>> >>> - per-process collection: >>> >>> [ perf record: Woken up 5 times to write data ] >>> [ perf record: Captured and wrote 1.079 MB perf.data (~47134 samples) ] >>> 2102.39user 153.88system 0:12.78elapsed 17645%CPU (0avgtext+0avgdata >>> 1187156maxresident)k >>> 0inputs+2272outputs (0major+1181660minor)pagefaults 0swaps >>> >>> Elapsed times look similar. Data file sizes differ significantly. >> >> Interesting. I wonder if that's because we're losing samples due to >> hammering the rb, or if that's a side-effect of this patch. >> >> Does perf report describe any lost chunks? >> >> For comparison, can you give --per-thread a go prior to these patches >> being applied? > > FWIW, I had a go with (an old) perf record on an arm64 system using > --per-thread, and I see that no samples are recorded, which seems like a > bug. > > With --per-thread, the slwodown was ~20%, whereas with the defaults it > was > 400%.
That looks similar to what I am observing in per-process single thread profiling >4x slowdown.
> > Thanks, > Mark. >
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