RFR (S): 8155229: Tune thread usage for live data clearing

[Mikael Gerdin]

Hi Thomas,

On 2016-04-28 13:16, Thomas Schatzl wrote:
> Hi all,
>
>    during testing of 8077144 I found that live bitmap clear can be
> significantly sped up by not using that many threads.
>
> A good conservative estimate (tends to use too many threads) that still
> cuts mark bitmap clear time by >50% is to give each thread at least 1
> MB of data to clear.
>
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8155229
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8155229/webrev/

The fix looks good.

One thing though,
now that I think about it, would it make sense to add an additional 
logging tag to

+  log_debug(gc, ergo)("Running %s using %u workers for " SIZE_FORMAT " 
work units.", cl.name(), num_workers, num_chunks);

Since these logging statements are not really about GC ergonomics but 
rather GC worker ergonomics.
This can be fixed further on too, I just want to hear if anyone else 
gets the same feeling.

/Mikael


> Testing:
> jprt, webrev, various performance tests
>
> Depends on 8155232.
>
> Thanks,
>    Thomas
>