RFR: JDK-8086056: ParNew: auto-tune ParGCCardsPerStrideChunk

[Thomas Schatzl]

Hi Tony,

On Wed, 2015-07-01 at 18:05 -0400, Tony Printezis wrote:
> Latest changes, as discussed with Bengt and Thomas,
>
> http://cr.openjdk.java.net/~tonyp/8086056/webrev.2/

  a few suggestions:

- please use braces even for simple statements in if-clauses, e.g. 

parNewGeneration.cpp:

 883   if (!UseDynamicParGCStrides) return;

- Comments should start with upper case:

parNewGeneration.hpp:

 354   // automatically calculate ParGCCardsPerStrideChunk based on the
old

- parameter calculation in ParNewGeneration::adjust_cards_per_stride:
  - DynamicParGCStridesMinSize should be > 0 (only if !
UseDynamicParGCStrides is enabled, not sure if that can be encoded
within the framework)
  - the issues with the Dynamic*Capacity variables Sangheon mentioned,
although I think it is fine that they are equal, just that "r" needs to
be set correctly.

Just wanting to check back if it was intended that the code always
rounds down, achieving the maximum stride only at the end of the
interval. E.g.
 
 912     const int stride_size_log = log2_long((jlong) stride_size);
 913     res = (size_t) 1 << stride_size_log;

It's fine with me, just asking.

Thanks,
  Thomas