linux os processor optimizations for OpenJDK GC performance enhancement

[Kim Barrett]

> On Apr 12, 2017, at 9:27 PM, Ram Krishnan <ramkri123 at gmail.com> wrote:
> 
> We are working on linux os processor specific optimizations centered around cache partitioning and better processor core thread(s) affinity for OpenJDK GC performance enhancement with the following benefits 
> - throughput increase
> - minimizing tail latency for latency sensitive applications
> - superior isolation in a multi-tenant environment
> 
> ​We have been looking at the G1GC code/documentation and performed some initial experiments. Based on this, what we understand is that STW events pause all application threads independent of which regions are being impacted by garbage collection. For example, if application thread "x" uses regions 1, 4, 5 and  garbage collection is working on regions 2 and 11, application thread "x" is paused during the STW event.
>  
> Your expert opinion on this topic is much appreciated.
> 
> -- 
> ​Thanks in advance,
> Ramki​

An application thread may touch memory in any region; there is no
notion of a thread being "scoped" to a specific set of regions. While
it might happen that a thread would only touch regions not being
worked on by the collector, there is no a priori way to know that.

If there were some way to allow collector access to a region while
blocking non-collector access, then it might be possible to defer
stopping application threads until they do a blocked access. But it's
not obvious such a scheme would actually be useful, as application
threads are likely to access young generation regions a lot, and those
regions are usually of interest during collector pauses.