Shenandoah Events

[zgu at redhat.com]

On Wed, 2019-01-30 at 10:54 -0500, Ken Dobson wrote:
> Hi Zhengyu,
> 
> We should still find out the impact when those events are being
> recorded to ensure it's not too significant. Would you be able to
> instruct me as to how to run the benchmarks so that I can measure the
> performance while the JVM is being recorded vs recording disabled?
Okay, we usually run specJVM and specJBB, do you have the benchmarks?
If not, where can I drop them?

For specJVM, the commandline I use:
${JAVA_HOME}/bin/java -jar jmh-specjvm2016.jar Derby  --jvmArgs "-Xmx1g 
-Xms1g -XX:+UnlockExperimentalVMOptions -XX:+UseShenandoahGC ..." -f 3

For specJBB, my script attached.

Thanks,

-Zhengyu 


> 
> Thanks,
> 
> Ken
> 
> On Tue, Jan 29, 2019 at 1:05 PM <zgu at redhat.com> wrote:
> > On Tue, 2019-01-29 at 18:25 +0100, Aleksey Shipilev wrote:
> > > On 1/29/19 6:03 PM, Ken Dobson wrote:
> > > > Just following up on the possibility of running the benchmarks
> > to
> > > > measure the performance overhead.
> > > > Please let me know if this would be possible and what I would
> > have
> > > > to do to get this done.
> > I was initially worry about the amount of region state transition
> > events generated. After adding should_commit() guard, I am now less
> > concerned.
> > 
> > Some overheads during recoding time, I think, are expected. So the
> > overhead, that we are talking about, is down to the additional
> > guard
> > test when recording is off, I doubt it is measurable.
> > 
> > Thanks,
> > 
> > -Zhengyu
> > 
> > 
> > > 
> > > It is possible, and should be as simple as running the benchmarks
> > > with/without -XX:+FlightRecorder?
> > > You are working with Zhengyu on JFR support, right? Zhengyu knows
> > how
> > > to run benchmarks.
> > > 
> > > > On Thu, Jan 24, 2019 at 11:28 AM Ken Dobson <kdobson at redhat.com
> > > > <mailto:kdobson at redhat.com>> wrote:
> > > >     The G1 version currently intercepts individual transitions
> > so
> > > > I'd hope they've measured the
> > > >     overhead and found it was acceptable but can't be certain
> > of
> > > > that. Yes I agree that's definitely
> > > >     the first step. Generally the default JFR profiling
> > > > configuration is ~2% overhead but detailed
> > > >     events such as these are not enabled in that configuration.
> > > > When using these events I think it
> > > >     would be best to disable all the default events and only
> > enable
> > > > the two Shenandoah Events to
> > > >     reduce the overhead. If you think measuring the benchmarks
> > is
> > > > the best way to get this data I'd
> > > >     be happy to do this if you can point me in the right
> > direction.
> > > 
> > > The first rule of benchmarking is not assuming anything,
> > including
> > > that someone else did them,
> > > especially for a different implementation.
> > > 
> > > There is also a bigger question: how much additional latency this
> > > brings to Shenandoah (tiny)
> > > pauses, when there are lots of transitions happen? Shenandoah
> > logs
> > > times with -Xlog:gc, and summary
> > > times with -Xlog:gc+stats.
> > > 
> > > -Aleksey