State of G1's "throughput barriers"?

Thomas Schatzl thomas.schatzl at
Tue Nov 12 09:41:57 UTC 2019

Hi Clemens,

On 09.11.19 15:54, Clemens Eisserer wrote:
> Hi,
> With great excitement I read about the proposal to add a
> throughput-mode to G1 - has there been any progress on this?
> In some cases the throughput overhead G1 introduced compared to CMS is
> quite noticeable, especially for the case where 2-5s pauses are quite
> tolerable - i really hoped to get an option to trade a bit of latency
> for better throughput.
> Thanks, Clemens

   the throughput barrier effort (or actually: optimize G1 when 
disabling refinement) afaict consists of two main steps:

- changing the existing barrier so that the throughput barrier is not 
completely different, allowing some interesting further optimizations.

This is mostly JDK-8087198 (currently out for review), and JDK-8226731, 
which improves the existing barrier already a bit.

- enabling the smaller barrier if concurrent refinement is disabled (via 
a new -XX:-G1UseConcRefinement). This is JDK-8134303 and ultimately 

Man Cao from Google is working on this, and it seems that we'll get at 
least the first big part soon. :)

Maybe Man wants to chime in for further details.


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