RFR (XS) 8215221: Serial GC misreports young GC time

[Aleksey Shipilev]

Hi Man,

Thanks for taking a look. New webrev:
  http://cr.openjdk.java.net/~shade/8215221/webrev.03/

Still passes hotspot tier1, eyeballing Dacapo logs, jdk-submit is running.


On 2/22/19 4:43 AM, Man Cao wrote:
> I found the following could fix the problem (yes, it's ugly, but I couldn't find cleaner way that
> works in all cases):
> 
> if (!do_young_collection) {
>   gc_prologue(complete);
>   increment_total_collections(complete);
> }
> if (!complete) {
>   increment_total_full_collections();
> }

I see, dang. Rewritten like this:

    if (!do_young_collection) {
      gc_prologue(complete);
      increment_total_collections(complete);
    }

    // Accounting quirk: total full collections would be incremented when "complete"
    // is set, by calling increment_total_collections above. However, we also need to
    // account Full collections that had "complete" unset.
    if (!complete) {
      increment_total_full_collections();
    }

> I also found that CollectedHeap._total_collections seems wrong with or without this change, for 
> SerialGC and CMS. It is smaller than the actual number of collections according to the GC ID.
> Reproduction recipe is the same as above.
Yeah, that minor thing needs to be fixed too, in a separate change.

-Aleksey


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