RFR(S): 8068579: Running with -XX:-UseParallelGC does not turn ParalleGC off (original) (raw)

Per Liden per.liden at oracle.com
Tue Mar 22 07:37:56 UTC 2016

Hi Jon,

On 2016-03-21 21:53, Jon Masamitsu wrote:

On 03/18/2016 03:12 PM, Per Liden wrote: Hi Jon,

On 18 Mar 2016, at 19:00, Jon Masamitsu <jon.masamitsu at oracle.com> wrote:

Per, http://cr.openjdk.java.net/~pliden/8068579/webrev.1/src/share/vm/runtime/arguments.cpp.frames.html

Why the change to make UseSerialGC as ergonomically selected? 1856 FLAGSETERGOIFDEFAULT(bool, UseSerialGC, true); This is to have a consistent way of selecting GC across all VM variants. We end up in this code when the user didn’t specify any GC, so the VM selects one based on various rules. The selection of SerialGC here is not really special or different from the other cases, it just happens to be the outcome of a very simple rule in minimal VMs. I didn't ask the question correctly. You used FLAGSETERGOIFDEFAULT() instead of (I think) FLAGSETDEFAULT(). Why did you want to add the "ERGO" attribute to the setting?

My reply above tried to answer this, but let's me rephrase and hope it becomes more clear.

Before this change, unless a GC was specified on the command-line the VM ergonomically select a GC using FLAG_SET_ERGO. There was however one exception to this, a minimal VM selected the SerialGC using FLAG_SET_DEFAULT. The change to also use FLAGS_SET_ERGO in minimal VMs is an attempt to make the way we select GC consistent across all VM variants. I.e. whenever the VM selects the GC for you we always use FLAG_SET_ERGO instead of like before where we sometimes use FLAG_SET_ERGO and sometimes FLAG_SET_DEFAULT. After all, ERGO means (to me at least) the VM made a decision for me.

I hope this helps.

cheers, Per

Jon

cheers, Per Jon

On 3/17/2016 6:36 AM, Per Liden wrote: Hi,

On 2016-03-16 09:12, Per Liden wrote: Hi Dima,

On 2016-03-15 17:38, Dmitry Fazunenko wrote: Hi Per,

A couple of comments: 1) globalsextension.hpp.frames.html requires copyright update 2) such fix should go with a regression test, it could be done separately. Good point. I was about to add a test for this just now and realized that the new semantics is not kept for minimal VMs (i.e. when INCLUDEALLGCS==0). I'll rework the patch a bit to have the same semantics also on minimal VMs. New webrev coming. Here's an updated webrev. The new semantics is now available on all VMs (including minimal). I also added a new test for this. This change also removes UNSUPPORTEDGCOPTION() and instead reuses the existing UNSUPPORTEDOPTION(), which I tweaked slightly to make the output more consistent across the code base. This in turn meant that I needed to adjust some other tests. http://cr.openjdk.java.net/~pliden/8068579/webrev.1/ Testing: jprt, manual thanks, Per thanks, Per Thanks, Dima

On 15.03.2016 16:48, Per Liden wrote: Summary: Explicitly disabling the default collector, without specifying another collector, will silently re-enable the default collector. This is a bit counter intuitive. A better approach would be for the VM to complain about the situation. Bug: https://bugs.openjdk.java.net/browse/JDK-8068579 Webrev: http://cr.openjdk.java.net/~pliden/8068579/webrev.0/ Testing: manual, jprt Example (assuming it's a platform/configuration with G1 as default): $ java -XX:-UseG1GC ... Today, the above command will happily start a VM with G1 enabled. With this patch the VM will instead complain, like this: $ java -XX:-UseG1GC ... Error occurred during initialization of VM Garbage collector not selected (default collector explicitly disabled) And of course, we're good with disabling the default collector as long as you specify some other collector, e.g.: $ java -XX:-UseG1GC -XX:+UseParallelGC ... cheers, Per

More information about the hotspot-gc-dev mailing list