RFR: 8199927: Make WhiteBox more GC agnostic (original) (raw)

Per Liden per.liden at oracle.com
Thu Mar 22 10:21:53 UTC 2018

On 03/22/2018 10:08 AM, Aleksey Shipilev wrote:

On 03/22/2018 10:04 AM, Per Liden wrote:

On 03/21/2018 04:03 PM, Aleksey Shipilev wrote:

This is a little dizzy, because I would have expected gc.isSelected() would tell me exactly what GC was being selected:

isAcceptable = gc.isSupported() && (gc.isSelected() || GC.isSelectedErgonomically()); ...so it should be just: for (GC gc : GC.values()) { map.put("vm.gc." + gc.name(), "" + gc.isSelected()); }

The way VMProps works and how the properties are set up can indeed make you a little dizzy. For example, vm.gc.Parallel=true doesn't necessarily mean that ParallelGC was "selected", just that it's an "acceptable" configuration. A test running with an explicit -XX:UseG1GC flag will get: vm.gc.Serial=false vm.gc.Parallel=false vm.gc.CMS=false vm.gc.G1=true And a test running with no explicit GC flag (which selects G1 ergonomically), will get: vm.gc.Serial=true vm.gc.Parallel=true vm.gc.CMS=true vm.gc.G1=true Ewww, messy. I naively thought vm.gc.* filters for jtregs are filtering based on what GC was actually running. But this is another thing to follow-up on. The patch itself looks good then.

To add to the confusion, there's also a vm.gc property, which only reflects what was explicitly specified on the command line. I don't quite see why it was done like this. I kind of hope we can clean that up some day. A single vm.gc property should be enough as far as I can tell, but maybe I'm missing something.

Anyways, thanks for reviewing!

/Per

-Aleksey

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