compatibility issue regarding the active processor count

Jon Masamitsu Jon.Masamitsu at Sun.COM
Wed Oct 1 06:53:53 PDT 2008

I would vote to have the new value be the default.  That's
based on the principle of "least surprise".  People who
need to think about such things probably already believe
they are getting the new value.

The number of default GC thread for the parallel collector
(UseParallelGC) was changed in HSX 12 (hotspot express) to
be consistent with the number of default threads used with
UseParNewGC/cms (CR 6362677).  So there has been a change
recently. I'll probably being hearing some complaints
about my change (hopefully not many), so I can include
the new calculation of the active number of processors
too, if relevant, in my explanations.  Not sure what
else beside GC will be affected by the new calculation
of active processors.

On 09/30/08 17:11, Xiaobin Lu wrote:
> Hi folks,
> I need your opinion about what we should do to solve the compatibility 
> issue regarding the active processor count. Basically, the problem is on 
> Solaris, if you create a processor set and then launch java process 
> without binding to that processor set, the number of available 
> processors to that java process is the total number of the online 
> processors minus the number of processors in the processor set you 
> created. Currently, we just report the total number of the online 
> processors as the active processor count which is wrong. This makes the 
> parallel garbage collector to behave in the wrong way (see bug 6749430 
> for details) and we need to fix it per request from CBOE.
> There may be a compatibility issue after we correct this wrong behavior 
> when someone has already depended on this wrong return, which we think 
> it might be rare. We definitely need to invent a new flag in order to 
> address this and the question is whether we should keep the current 
> behavior as default or not. Personally, I feel we should have that flag 
> to fall back to the current wrong behavior, but I might be wrong.
> Thanks so much in advance for your opinion.
> -Xiaobin

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