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

[Roman Kennke]

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/webre
> 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
> 
>