Shenandoah Events

[Aleksey Shipilev]

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.

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