RFR (S): Sorting the regions for collection set takes a while during pause

[Roman Kennke]

Duh. We don't even seem to stop at the first region that exceeds the
threshold. This whole sorting seems not necessary, and lots of wasted
space too (for the _sorted_regions list).

Roman

Am Donnerstag, den 26.01.2017, 18:48 +0100 schrieb Aleksey Shipilev:
> Maybe! Let's see...
> 
> -Aleksey
> 
> On 01/26/2017 06:43 PM, Roman Kennke wrote:
> > Or maybe not sort the list at all? Downside: we need to scan all
> > regions and decide on their garbage, instead of stopping at the
> > first
> > region that exceeds the garbage threshold. Upside: no sorting
> > necessary. May be worth a try.
> > 
> > Roman
> > 
> > 
> > Am Donnerstag, den 26.01.2017, 18:39 +0100 schrieb Aleksey
> > Shipilev:
> > > Hi,
> > > 
> > > Profiled the pause-intensive application for fun, and spotted an
> > > easy
> > > optimization target. In final mark pause, we select collection
> > > set,
> > > and for
> > > that, we sort the regions by garbage. This incurs (N log N) calls
> > > to
> > > comparator,
> > > which calls SHHR->garbage() and handles nulls, etc.
> > > 
> > > Doing a simple trick:
> > >  http://cr.openjdk.java.net/~shade/shenandoah/pause-sort-better/w
> > > ebre
> > > v.01/
> > > 
> > > ...improves timings:
> > > 
> > > before:
> > > 
> > >   Final Mark Pauses (gross) = 7.05 s (a = 1059 us) (n =  6659)
> > >     (lvls, us = 717, 805, 830, 912, 9376)
> > > 
> > >   Final Mark Pauses (net)   = 3.03 s (a =  454 us) (n =  6659)
> > >     (lvls, us = 102, 211, 221, 270, 8728)
> > > 
> > >   Prepare Evacuation = 2.04 s (a = 306 us) (n =  6659)
> > >     (lvls, us = 273, 293, 297, 301, 1490)
> > > 
> > > after:
> > > 
> > >   Final Mark Pauses (gross) = 6.12 s (a = 851 us) (n =  7195)
> > >     (lvls, us = 547, 605, 629, 689, 5335)
> > > 
> > >   Final Mark Pauses (net)   = 3.15 s (a = 438 us) (n =  7195)
> > >     (lvls, us = 98, 203, 211, 260, 4877)
> > > 
> > >   Prepare Evacuation = 0.75 s (a = 105 us) (n =  7195)
> > >     (lvls, us = 82, 96, 105, 109, 187)
> > > 
> > > 0.2 ms off the already low pause time.
> > > 
> > > Thanks,
> > > -Aleksey
> > > 
> > > 
> 
>