G1 has more expensive GC write barriers - if you have a reference heavy heap with lots of mutation, it can add up. 20% more overhead for each barrier is a number I've heard before.
On Monday, October 31, 2016, Peter <graphhop...@gmx.de> wrote: > Hi Bernd, > > why do you think it is measuring a short workload? 'short' in which terms? > The overall test suite takes roughly 3 minutes but can be increased easily > via increasing the number of road routing queries. BTW: with routing.mean > we measure the latency of every road routing query, at least I think so ;) > > > Did you check the verbose GC logs, and how many CPUs does Java see/use? > > Nothing suspicious in the GC logs > <https://gist.github.com/karussell/94848aa48244252c6010018b3621b565> IMO, > except that G1 produces much more output. Still this reminded me of another > mistake <http://stackoverflow.com/q/38905739/194609> I made recently (not > disabling swapping) and so I went to my dev server (instead of laptop) > where this is already done and have more RAM there (32g), still using just > 1000m and the results are a bit better: 320ms vs. only 235ms, so G1 is only > ~25% slower. What differences are expected here ... let's say 'maximum'? > > BTW: CPU usage on the server is roughly 200-240% for G1 and 100-120% for > the parallel GC, so the speedup might be also related to the CPUs as the > laptop only has 2 cores without hyperthreading. > > Regards > Peter > > On 31.10.2016 20:52, Bernd Eckenfels wrote: > > Hello, > > Since this is measuring a short workload after vom startup it might not be > the best benchmark, but then again throughput GC is expected to be faster > than G1. > > In the particular case however I guess you could tune G1 a bit to that > workload. Did you check the verbose GC logs, and how many CPUs does Java > see/use? > > Gruss > Bernd > -- > http://bernd.eckenfels.net > > > > > On Mon, Oct 31, 2016 at 8:38 PM +0100, "Peter" <graphhop...@gmx.de > <javascript:_e(%7B%7D,'cvml','graphhop...@gmx.de');>> wrote: > > Hi, >> >> I've stumbled today* over a big speed difference for code execution with >> G1 GC vs. parallel GC also in the latest JDK8 (1.8.0_111-b14). Maybe you >> have interests to investigate this. You should be able to reproduce this >> via: >> >> # setup >> git clone https://github.com/graphhopper/graphhopper >> wget http://download.geofabrik.de/europe/germany/bayern-latest.osm.pbf >> cd graphhopper >> >> # run measurement >> export JAVA_OPTS="-XX:+UseParallelGC -Xmx1000m -Xms1000m" >> # the graphhopper.sh script just makes the installation of maven and >> bundling the jar a bit simpler >> # you can also execute the tests in the class Measurement.java >> <https://github.com/graphhopper/graphhopper/blob/master/tools/src/main/java/com/graphhopper/tools/Measurement.java> >> ./graphhopper.sh clean >> ./graphhopper.sh measurement berlin-latest.osm.pbf >> # now a measurement-<some date>.properties is created: >> grep routing.mean measurement-XY.properties >> >> Now this should print a line where the value is in ms. E.g. I get ~450ms >> for the parallel GC and ~780ms for G1GC (on an old laptop). When I increase >> the Xmx for the G1 run to 1400m the results do NOT get closer to parallel >> GC! >> >> Let me know if you need more information! >> >> Regards >> Peter >> >> * >> https://github.com/graphhopper/graphhopper/issues/854 >> >> -- >> GraphHopper.com - fast and flexible route planning >> >> > > -- > GraphHopper.com - fast and flexible route planning > > -- Sent from my phone
_______________________________________________ hotspot-gc-use mailing list hotspot-gc-use@openjdk.java.net http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use
