Shenandoah Events

[Ken Dobson]

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?

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
>