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

[Thomas Schatzl]

Hi Mikael,

  thanks for your review.

On Thu, 2016-04-28 at 16:28 +0200, Mikael Gerdin wrote:
> 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.

Still ergonomics :)

Maybe something like log_debug(gc, ergo, workers), so by gc+ergo*=debug
you can enable all of them?

> This can be fixed further on too, I just want to hear if anyone else 
> gets the same feeling.

Thanks,
  Thomas