CMS option for Java7 ignored (was Re: 1.7 G1GC significantly slower than 1.6 Mark and Sweep?)

Bengt Rutisson bengt.rutisson at oracle.com
Mon May 2 00:00:50 PDT 2011


John,

>> .... I don't know how to activate CMS for Java 7, it ignores the option that I'd use
>> for Java 6.
> ...
>> Java6: -ea -Xms256M -Xmx256M -XX:UseConcMarkSweepGC -verbose:gc
> ...

What do you mean when you say "ignores"? Does the VM start and just 
ignores your option or does the VM complain that it is an unknown option?

I am asking since the error message that you get if you use the command 
line that you posted is somewhat confusing. Maybe this is just a typo in 
the email, but your command line is missing the plus sign in front of 
UseConcMarkSweepGC. If you run the command line from your email you get 
this error message:

Unrecognized VM option 'UseConcMarkSweepGC'
Could not create the Java virtual machine.

Which, I admit, is confusing. The VM does recognize the option, what is 
missing is just the value for the option. If you use this command line 
instead you get CMS and no error message:

-Xms256M -Xmx256M -XX:+UseConcMarkSweepGC -verbose:gc

But then again, maybe this was not what you were asking...

Bengt




>>>>>> For 1.6.0_22: -Xms256M -Xmx256M -XX:+UseConcMarkSweepGC
>
> Are you saying that if you do:
>
>      -Xms256M -Xmx256M -XX:UseConcMarkSweepGC -verbose:gc
>
> you do not get CMS? If not, what does the GC log say?
> Can you provide the following details:
>
> % java -version
>
> and also
>
> % jinfo<pid>
>
> as well as:
>
> % jnifo -flag UseConcMarkSweepGC<pid>
>
> where<pid>  is yr JVM process.
>
> The main issue will be dealt with in the original thread.
> Sorry for the digression.
>
> -- ramki
> _______________________________________________
> hotspot-gc-use mailing list
> hotspot-gc-use at openjdk.java.net
> http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use

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